Molten-salt-heated indirect screw-type thermal processor

ABSTRACT

A body of heat transfer fluid circulates in a first loop through an indirect screw-type thermal processor, a rundown tank, a pump, a heater and a fill tank, continuously heating the processor. With the pump operating, a first vertical distance between the fill tank bottom and the processor under the influence of gravity sets a minimum fluid pressure at the processor; a stem pipe opening in the fill tank at a second vertical distance above the processor sets a maximum pressure. With the pump inactive, the entire body of fluid passively drains to the rundown tank. Supplying the fluid may entail melting a salt, hydrating a salt, or both; such may be done in the rundown tank before circulation through the processor begins. A hydrated salt may be circulated, then heated and dehydrated, to gradually warm the processor. A dehydrated salt may be rehydrated and then stored; this may be done in the rundown tank after ceasing circulation through the processor. Also described: misting hydration and variable-speed-pump pressure regulation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of thermalprocessing of materials, more particularly to thermal processing byindirectly heating a process material in a processor, and especially tomolten-salt-heated indirect screw-type thermal processors.

2. General Background and State of the Art

U.S. Pat. No. 8,739,963 describes one of many available screw-typethermal processors.

Chinese Utility Model CN203479118U discloses a molten salt energystorage system capable of gravity flow salt evacuation withoutdependence on a salt evacuation pump.

INVENTION SUMMARY

It is an object of the present invention to provide superior performanceand cost-effectiveness in the indirect thermal processing of materials.

It is also an object to provide a fluid-heated indirect thermalprocessor from which a hot heat transfer fluid, which would solidify orbecome unworkably viscous upon cooling to ambient temperature, willdrain passively before solidifying in the event that its circulationthrough the processor is interrupted.

It is also an object to provide a fluid-heated indirect thermalprocessor which operates safely and economically, with heat transferfluid circulating at temperatures in excess of 800° F., as high as 1100°F., and even higher, should salts usable at such temperatures becomeavailable to the apparatus, even when the heat transfer fluid iscorrosive and has a solidification temperature as high as 480° F.

It is also an object to provide a fluid-heated indirect thermalprocessor in which the thermal processor—the portion of the apparatuswhich transfers heat from a heat transfer fluid to a feed material whileconveying the feed material from a feed inlet to a feed outlet—isconstructed and operated without any need of ASME pressure boundarycertification. For example, in some cases the processor should heattransfer fluid at a pressure very near ambient pressure, i.e., at lessthan 1 bar, and should not be exposed directly to any source ofhigh-pressure such as a heat transfer fluid circulation pump or thelike.

It is also an object to provide a fluid-heated indirect thermalprocessor that operates safely and economically without dependency on ahigh-powered electric heating system in addition to a combustion heatingsystem. Such independence in some cases avoids costs associated withaccess to a regional power grid and costs associated with redundantheating systems.

It is also an object to provide a fluid-heated indirect thermalprocessor that operates safely and economically without any need for aheat trace on the piping or on the processor itself.

It is also an object to provide a fluid-heated indirect thermalprocessor which operates safely and economically when started with cold,dehydrated salt, with cold, hydrated salt, or with hot hydrated ordehydrated salt. The apparatus should be able to hydrate a salt on-site,starting with hot or cold dehydrated salt. The apparatus also should beable to reach operating temperature gradually enough to avoid thermalshock to any part of the apparatus, especially the thermal processor,even if both hydration and dehydration of a salt are called for in anoperating cycle. The apparatus should be capable of controlled shutdownwith prompt, safe, passive disposal of hot salt at a low point in thesystem followed, if desired, by gradual hydration of hot salt forstorage and for later re-starting from ambient temperature withoutprolonged melting.

In accordance with these objects and with others which will be describedand which will become apparent, an exemplary embodiment ofmolten-salt-indirectly heated screw-type thermal processing apparatushas an indirectly heated screw-type thermal processor; a heater; arundown tank; and a pump. The apparatus requires an operating volume ofa heat transfer fluid for transferring heat from the heater to thethermal processor. The thermal processor has a heat transfer fluid inletfluidly communicating with the heater and a heat transfer fluid outletfluidly communicating with the rundown tank. The rundown tank has afluid-containing portion dimensioned to hold at least the operatingvolume and has a rundown tank headspace portion above thefluid-containing portion. The rundown tank headspace portion is equippedto relieve a pressure differential between the rundown tank and theambient environment.

The pump, the heater, the thermal processor and the rundown tank areoperatively connected so as, when the pump is active, to establish aheat transfer circulation loop through the heater and the thermalprocessor.

The pump, the heater, the thermal processor and the rundown tank areoperatively connected so as, when the pump is inactive, to establish thefluid-containing portion as the fluid passive drainage destinationrelative to the pump, the heater and the thermal processor.

Another exemplary embodiment has a gravity tube, a gravity tube upperdrain, a gravity tube gas orifice, and a gravity tube lower drain. Thegravity tube fluidly communicates with the heat transfer fluid inlet ata first height. The gravity tube fluidly communicates with the heater ata second height, the second height being above the first height.

The gravity tube upper drain also fluidly communicates with the gravitytube at a third height, the third height being above the second height.The gravity tube upper drain fluidly communicates with the rundown tank.The gravity tube gas orifice fluidly communicates with the gravity tubeat a fourth height, the fourth height being above the third height. Thegravity tube gas orifice also fluidly communicates with the rundown tankheadspace portion (and may be regarded as having, e.g., a connector tuberunning to the rundown tank headspace portion for this purpose).

The gravity tube lower drain fluidly communicates with the gravity tubeat a fifth height, the fifth height being below the first height. Thegravity tube lower drain fluidly communicates with the rundown tank at asixth height, the sixth height being below the fifth height.

Another exemplary embodiment has a restrictor located in the gravitytube lower drain at a seventh height, the seventh height between thefifth height and the sixth height. The restrictor is dimensioned torestrict fluid conducting capacity of the gravity tube lower drain,thereby assuring that most of the fluid flows through the processorwhile enough fluid flows through the restrictor to keep the gravity tubelower drain hot, preventing solidification and obstruction.

In another exemplary embodiment, the gravity tube has a fill tank andthe gravity tube upper drain has a stem pipe, the fill tankcommunicating with the gravity tube at the second height, the stem pipefluidly communicating with the fill tank at the third height and fluidlycommunicating with the gravity tube upper drain.

Another exemplary embodiment is selectively configurable to establish apreheating fluid circulation loop through the rundown tank and theheater and to interrupt the heat transfer circulation loop, so that suchprocesses as melting, heating and hydration can be conducted within therundown tank or within a loop between a heater and the rundown tankwhile the fluid is not circulating through the processor. Preferably, atleast one heater is situated in the preheating fluid circulation loop.

In another exemplary embodiment, the rundown tank is equipped with aheat trace, the heat trace being coextensive with the preheating fluidcirculation loop through the rundown tank, so that a path is availablefor circulating fluid, even when most of the fluid in the rundown tankhas cooled and solidified.

Another exemplary embodiment has a fluid hydrator and a hydration fluidsupply. The fluid hydrator fluidly communicates with the processorpreheating fluid circulation loop and with the hydration fluid supply.The hydration fluid supply is selected from among a supply of water, asupply of steam, and a supply of a hydrating liquid solution.

In another exemplary embodiment, the fluid hydrator has a nozzle,located in the rundown tank headspace portion, configured to gentlydeposit a hydration fluid in the rundown tank, so that, for example, amolten salt can be hydrated without disrupting the fluid surface andsplattering the fluid in the tank.

In another exemplary embodiment, the fluid hydrator has a sparge tubelocated in the fluid-containing portion of the rundown tank.Alternatively, the fluid hydrator has an eductor located somewhere inthe preheating fluid circulation loop or in the heat transfercirculation loop.

Another exemplary embodiment is adapted for a heat transfer fluid havinga melting point and a density. The first height and the second heightare selected such that a column of the heat transfer fluid extendingvertically from the first height to the second height exerts pressure atthe second height no greater than 14.9 PSIG when the fluid is at themelting point.

Another exemplary embodiment has at least one external heater located atleast partially outside the rundown tank, the preheating fluidcirculation loop passing through the external heater.

Another exemplary embodiment has a pressure sensor proximate the heattransfer fluid inlet of the thermal processor and a pump variable speedcontrol, the pump variable speed control being operatively coupled withthe pressure sensor so as to slow the pump when the pressure sensorreports a pressure approaching 14.9 PSIG.

In an exemplary embodiment, the heat transfer fluid outlet is locatedabove the first height and a path is provided from the heat transferfluid inlet for passive drainage to the rundown tank when the pump isinactive.

In an exemplary embodiment, a vacuum breaker fluidly communicates withthe heat transfer fluid outlet, preventing vacuum lock interference withdrainage of fluid from the processor and preventing vapor lockinterference with entry of fluid into the processor.

In an exemplary embodiment, the rundown tank has a sump and a heattrace; the pump has a pump inlet located in the sump or near enoughthereto to ingest fluid heated by the heat trace.

In an exemplary embodiment, underpressurization of the rundown tank isrelieved by introduction of a padding gas, preferably an inert paddinggas such as nitrogen to avoid contaminating a molten salt withcarbonates formed from atmospheric carbon dioxide.

Also in accordance with the above objects, a method of operating amolten-salt-indirectly heated screw-type thermal processor includes thesteps of:

providing a molten-salt-indirectly heated screw-type thermal processor,the thermal processor having an operating heat transfer fluidtemperature range, an operating heat transfer fluid flow rate range andan operating heat transfer fluid pressure range;

providing a body of heat transfer fluid, a heater, and a rundown tank,

the heat transfer fluid being capable of conveying heat from the heaterto the thermal processor at a temperature within the operating heattransfer fluid temperature range while flowing into the thermalprocessor at a heat transfer fluid flow rate within the operating heattransfer fluid flow rate range at a pressure within the operating heattransfer fluid pressure range,

the heater being capable of heating the heat transfer fluid sufficientlyat the flow rate and temperature,

the body of heat transfer fluid having volume at least sufficient tooperate with the heater and the thermal processor,

the rundown tank having capacity more than sufficient to contain all ofthe body of heat transfer fluid;

delivering the heat transfer fluid from the heater to the thermalprocessor at the temperature, the flow rate and the pressure whiledelivering the heat transfer fluid from the thermal processor to theheater; and

after the steps of delivering, passively disposing the body of heattransfer fluid in the rundown tank.

An exemplary instance of the method may include, before the step ofdisposing, a step of producing the heat transfer fluid by melting asolid. While melting the solid, the fluid generated by melting can insome exemplary instances of the method be circulated within or throughthe rundown tank. In some exemplary instances, this circulation is donewhile interrupting the heat transfer circulation loop, so that theprocessor is not exposed to the fluid at that time.

Also in an exemplary instance of the method, the method may be carriedout with a heat transfer fluid comprising a melting-point-alteringmaterial selected from among: water, a hydrating fluid, a dopant. Such afluid could, for example, be delivered ready-made or produced nearby forintroduction into the apparatus.

In an exemplary variation, before the step of disposing, there is a stepof producing the heat transfer fluid by adding to a salt amelting-point-altering material selected from among: water, a hydratingfluid, a dopant. A preliminary step of melting a solid may be added ifthe fluid has solidified.

In an exemplary instance, after the step of disposing, there is a stepof adding to the heat transfer fluid a melting-point-altering materialselected from among: water, a hydrating fluid, a dopant, so that thefluid can be stored as a hydrated liquid. This is convenient when, forexample, a stored solidified dehydrated salt would require prolongedsteps of melting and hydration the next time the apparatus is operated.

In a variation of the method, the heat transfer fluid comprises a saltwhich is at least partially hydrated and which is at least partlydehydrated before the step of disposing the solution in the rundowntank. It is often preferable to dehydrate the salt fluid before orduring the step of delivering the fluid to the processor.

The step of dehydrating and the step of delivering may be at leastpartially simultaneous. In an exemplary method, the thermal processorhas a predetermined maximum tolerable rate of temperature increase, thesalt has a melting temperature which increases with decreasinghydration, and the step of dehydrating occurs at a rate such that thethermal processor is warmed at a rate no greater than the maximumtolerable rate of temperature increase.

An exemplary method may be carried out with the step of deliveringincluding steps of measuring the pressure, computing a correction of thepressure, and delivering the heat transfer fluid to the thermalprocessor at a flow rate adjusted to effect the correction of thepressure.

Preferably, in an exemplary method, the step of delivering includes astep of elevating the heat transfer fluid relative to the thermalprocessor so as to establish a gravity fluid pressure head with the heattransfer fluid entering the thermal processor at a pressure at leastwithin the operating heat transfer fluid pressure range.

In a highly preferred method, the step of delivering includes a step ofpassively diverting the heat transfer fluid to bypass the thermalprocessor in an amount sufficient to prevent the pressure exceeding theoperating heat transfer fluid pressure range.

In an exemplary instance, a fill tank fluidly communicates with theheater and with the thermal processor; a stem pipe fluidly communicateswith the fill tank and with the rundown tank; the step of elevatingincludes accumulating the fluid in the fill tank; and the step ofpassively diverting includes directing the fluid via the stem pipe tothe rundown tank.

An exemplary instance is carried out with a thermal processor having aheat transfer fluid inlet at a lower elevation than the heat transferfluid outlet. In the step of delivering, the fluid enters the thermalprocessor via the heat transfer fluid inlet and exits the thermalprocessor via the heat transfer fluid outlet. In the step of disposing,the fluid exits the thermal processor via the heat transfer fluid inlet.

In an exemplary instance, a vacuum breaker fluidly communicates with theheat transfer fluid outlet. In the step of disposing, a gas enters thethermal processor via the vacuum breaker.

In an exemplary instance, the rundown tank has a rundown tank headspaceportion and the vacuum breaker fluidly communicates with the rundowntank headspace portion.

In an exemplary instance, the fill tank has a fill tank headspaceportion; the rundown tank has a rundown tank headspace portion; and aheadspace connector fluidly communicates with the fill tank headspaceportion and the rundown tank headspace portion.

In an exemplary instance, the operating heat transfer fluid pressurerange is from −12 PSIG to 14.9 PSIG, inclusive.

An exemplary instance has, during the step of melting, a step ofmeasuring a temperature of the solid being melted and a step ofinitiating the step of delivering when the temperature has reached apredetermined value.

In an exemplary instance, during the step of melting, there is a step ofmeasuring a temperature of the solid being melted and a step ofinitiating the step of adding when the temperature has reached apredetermined value.

In an exemplary instance, during the step of dehydrating, steam isvented from the rundown tank headspace portion.

In an exemplary instance, the rundown tank has a rundown tank headspaceportion and there is a step of supplying a padding gas to the rundowntank headspace portion when the rundown tank headspace portion isunderpressurized relative to the ambient environment and a step ofventing a gas from the rundown tank headspace portion when the rundowntank is overpressurized relative to the ambient environment. In anexemplary instance, during the step of dehydrating, steam is vented fromthe rundown tank headspace portion.

In an exemplary instance, during the step of disposing, there is a stepof conducting a gas from the rundown tank headspace portion to thethermal processor fluid outlet via the vacuum breaker.

In an exemplary instance, the rundown tank has a rundown tank headspaceportion. During the step of delivering, there is a step of conducting agas from the thermal processor to the rundown tank headspace portion.

In an exemplary instance, during the step of adding, there is a step ofmeasuring a melting-point-altering material content of the heat transferfluid and a step of initiating the step of delivering when the materialcontent has reached a predetermined value.

In an exemplary, although not necessarily preferred instance of themethod, a step of hydrating a dehydrated salt heat transfer fluid isbegun while the fluid is circulating in the heat transfer circulationloop, rather than after the fluid has passively drained to the rundowntank.

From experience with the dangers of rupturing a vessel containing moltenheat transfer fluid, and mindful of the cost and operational limitationsencountered when designing and building thermal processing apparatuswith the types of steel that are certifiable for use as pressureboundary materials, the inventors sought a low-cost, high-reliabilitymethod of ensuring that heat transfer fluid is never delivered to thethermal processor at a pressure requiring a pressure boundary material.The present invention assures that the fluid is delivered to the thermalprocessor from a source which derives its pressure from a fluid columnheight under the influence of gravity and not directly from a pump orother source which could deliver higher pressures. The present inventionalso assures that, when pumping ceases, fluid located in the gravitytube and fluid located in the thermal processor will drain passively,rather than remaining in place and solidifying in place.

Mindful of a customer's interest in lowering costs of operating inremote rural locations, the inventors sought to avoid any dependency onpower in or on a fail-safe pumping system to prevent costly andexpensive solidification of molten salt heat transfer fluid inside thethermal processor or inside the piping to or from a heater. The presentinvention ensures prompt, passive draining of heat transfer fluid fromthe thermal processor, heater and gravity tube whenever pumping ceases.In the present invention, the rundown tank provides a reservoir at a lowpoint in the apparatus. The rundown tank can receive fluid on its wayfrom the thermal processor back to the heater. The rundown tank canreceive drainage from any part of the apparatus at any time drainage isdesired. The rundown tank can have a headspace which serves as a gasreservoir and which can be fluidly connected with, e.g., the heater, thefill tank, and the thermal processor.

By setting the first and second heights to limit pressure at theprocessor fluid inlet to no greater than 14.9 PSIG, the presentinvention tailors the processor fluid inlet pressure to the object ofavoiding the necessity of using ASME pressure boundary materials andconstruction.

The inventors chose to equip the rundown tank to vent a gas to theambient environment and to receive a gas from a source selected fromother parts of the apparatus or from a padding gas supply. Beingfamiliar with the special requirements of various heat transfer media,they sought to avoid deleterious effects of carbon dioxide and oxygenabsorbed from the atmosphere. When the heat transfer fluid is chemicallyand physically compatible with the constituents of the Earth'satmosphere, such as when the molten salts are below 850° F. in theenvironment in question, air can be admitted through the gravity tubegas orifice. When it is preferable to close the system, a connector canbe used to assure fluid communication between the gravity tube gasorifice and a headspace of another component of theapparatus—preferably, the rundown tank, also in some cases a fill tank.Pressure differentials between the respective headspaces of suchcomponents as a thermal processor, a fill tank and a heater can berelieved in this manner, relieving local and systemic pressuredifferentials while in many cases avoiding loss of gas to theenvironment or intrusion of atmosphere from the environment. When theoperational cycle of the apparatus at times requires the introduction ofa gas to compensate for an overall pressure reduction in the apparatus,a padding gas, e.g., nitrogen, is introduced via the gravity tube gasorifice or through a similar orifice in, e.g., a headspace of a rundowntank or thermal processor.

Exemplary embodiments of the apparatus in accordance with the presentinvention include a gravity tube and a gravity tube upper drain. Someembodiments also include a fill tank and a stem pipe. The inventorswished to provide a consistent source of heat transfer fluid to thethermal processor, even when the rate of delivery of such fluid from theheater fluctuates. This arrangement delivers heat transfer fluid from anelevated reservoir at a head of pressure proportional to the differencebetween the height of the fluid level in the fill tank and the height ofthe heat transfer fluid inlet of the thermal processor. As long asenough fluid is being delivered to keep the gravity tube fed, thepressure at the thermal processor fluid inlet will be within a narrowrange. The total column height from the stem pipe opening to the heattransfer fluid inlet sets the upper limit of the range; the total columnheight between the bottom of the fill tank and the heat transfer fluidinlet 38 sets the lower limit. When a gross excess of fluid is deliveredto the fill tank, the stem pipe efficiently drains the excess to therundown tank. When pumping ceases, fluid in the fill tank and fluid thathas already entered or passed through the gravity tube will drainpassively, one way or another, under the influence of gravity.

In some exemplary embodiments the rundown tank disposes the fluid volumeso as to provide a fluid upper surface suitable for hydration by gentledeposition of water mist on the surface. The inventors found sufficientsurface area for hydration to be important, because it facilitates theuse of salts which have high operating temperatures and correspondinglyhigh melting temperatures. The inventors, wishing to avoid splatteringmolten salt during hydration, arranged for the hydration water dispenserto provide a mist fine enough not to disrupt the surface of the salt.

The rundown tank has a headspace. Gas may flow from the rundown tankheadspace to the gravity tube gas orifice, so that air and its carbondioxide and oxygen constituents are not drawn into the system. Theinventors sought to avoid the formation of carbonates in the salt.

In an embodiment having a rundown tank, the rundown tank is equipped toheat the fluid, and the pump and the rundown tank are configuredselectively to circulate the fluid between the pump and the rundowntank. The inventors were aware of difficulties that attend the operationof fluid-heated indirect thermal processors. With a heat transfer fluidwhich is a salt that solidifies at a temperature well above ambient,such as 288° F. or 448° F., it may be necessary to start the apparatusafter the salt has cooled and solidified in the rundown tank. Sometimes,it is desirable to heat a portion of the rundown tank surrounding a pumplocated there until a small volume of salt has liquefied, start thepump, and recirculate the salt to the rundown tank via the bypassbranch. When enough salt has liquefied, the heater can be started andliquefied salt can be delivered to the thermal processor.

In some applications, the inventors contemplate the use of a salt whichhas a high melting point—so high, that a cold thermal processor wouldnot withstand the temperature gradients caused by the abruptintroduction of the melted salt. The inventors solved this problem byrecognizing that the in some cases the salt may be hydrated, loweringthe temperature at which it liquefies. To provide water for hydration,the rundown tank has a set of water misting nozzles. The process ofhydrating a salt may be started with hot salt at a time when the salt iscirculating in the apparatus at a high temperature after warming coldsalt in the rundown tank. However, it is preferable to hydrate the saltin the rundown tank, using the water misting nozzles while recirculatingthe salt to the rundown tank. At shutdown, hot dehydrated salt isdrained to the rundown tank; if rehydration is desired, it is done byrecirculating fluid to the rundown tank with the rundown tank vent openand the nozzles activated, beginning hydration at about 300° F. for somesalts and about 500° F. for others, and continuing until the salt isfully hydrated at a temperature close to ambient.

An exemplary embodiment of the apparatus has a restrictor located in thegravity tube lower drain at a seventh height below the first height andabove the fifth height. The inventors intended that only enough fluidwould drain through the restrictor to keep this path heated, therebykeeping it open. An additional requirement, however, was that passivedrainage be accomplished before salt in the apparatus has time tosolidify. In the present invention, the restrictor directs most of thefluid flow to the thermal processor. Only a small fraction of the fluidflow drains through the restrictor. Nevertheless, this fraction is largeenough to permit passive drainage of molten salt to be completed inabout 30 minutes.

In an exemplary embodiment of the apparatus, the heat transfer fluidoutlet is located above the first height, i.e., the level of theprocessor fluid inlet. The processor is inclined or otherwise soconstructed that the fluid drains passively out the processor fluidinlet when pumping has stopped. With a vacuum breaker or a headspaceconnector fluidly communicating with the heat transfer fluid outlet at arelative high point, any vapor lock during filling or vacuum lock duringdrainage can be relieved.

The method is practicable even when it includes, while the pump isactive, a step of circulating the fluid in the apparatus at atemperature in excess of 1000° F.

Also in accordance with the present invention, an exemplary embodimentof a phase-separating pressure modulator for molten-salt-indirectlyheated screw-type thermal processing apparatus comprises a fill tankhaving a fill tank bottom portion; a heater output tube fluidlycommunicating with the fill tank at the fill tank bottom portion; agravity tube fluidly communicating with the fill tank at the fill tankbottom portion and fluidly communicating with a fluid deliverydestination; a stem pipe fluidly communicating with the fill tank at anelevation above the fill tank bottom portion; a fill tank headspaceportion defined as a portion of the fill tank above the elevation; and afill tank headspace vent fluidly communicating with the fill tankheadspace portion and with a fluid drainage destination. Preferably, thedrainage destination is a rundown tank and the fluid deliverydestination is a thermal processor.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the objects and advantages of the presentinvention, reference should be had to the following detaileddescription, taken in conjunction with the accompanying drawing, inwhich like parts are given like reference numbers and wherein:

FIG. 1 is a schematic representation of A FIRST EXEMPLARY EMBODIMENT ofa molten-salt-indirectly heated screw-type thermal processing apparatusin accordance with the present invention;

FIG. 2 is a schematic representation of SECOND and THIRD EXEMPLARYEMBODIMENTS thereof;

FIG. 3 is a schematic representation of A FOURTH EXEMPLARY EMBODIMENTthereof;

FIG. 4 is a schematic representation of A FIFTH EXEMPLARY EMBODIMENTthereof;

FIG. 5 is a schematic representation of A SIXTH EXEMPLARY EMBODIMENTthereof;

FIG. 6 is a schematic representation of A SEVENTH EXEMPLARY EMBODIMENTthereof; and

FIG. 7 is a schematic representation of AN EIGHTH EXEMPLARY EMBODIMENTthereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described. FIG. 1 illustrates in schematicview A FIRST EXEMPLARY EMBODIMENT of a molten-salt-indirectly heatedscrew-type thermal processing apparatus in accordance with the presentinvention, shown generally at 20, having fluidly interconnected athermal processor 22, a rundown tank 24, a pump 26, and a heater 28.

The thermal processor 22 has heat transfer fluid spaces 32 with heattransfer fluid inlets 38 and heat transfer fluid outlets 84. The thermalprocessor 22 has a process space 34 with a process material inlet 82 anda process material outlet 86. A fluid outlet drain tube 85 fluidlyconnects the heat transfer fluid outlets 84 to the rundown tank 24. Thethermal processor 22 is configured to transfer heat between the heattransfer fluid spaces 32 and the process space 34. A body of heattransfer fluid 25 (fluid 25) is shown in the rundown tank 24.

A processor fluid inlet tube 87 fluidly connects the heat transfer fluidinlets 38 with the heater output tube 80 of the heater 28. Heat transferfluid 25 flows from the heater 28, enters through the heat transferfluid inlets 38, flows through the heat transfer fluid spaces 32, andexits through the heat transfer fluid outlets 84. The heat transferfluid spaces 32 are passively drainable. The heat transfer fluid spaces32 are configured to deliver fluid 25 passively to the rundown tank 24via the fluid outlet drain tube 85.

A conveyor 90 is disposed in the process space 34. Process materialenters through the process material inlets 82, receives heat from theheat transfer fluid spaces 32 while the conveyor 90 moves it through theprocess space 34, and exits through the process material outlet 86. Asillustrated, the conveyor 90, which is disposed within the process space34, includes one of the heat transfer fluid spaces 32. Another 32surrounds the process space 34.

The pump 26 is configured to propel fluid 25 from the rundown tank 24 tothe heater 28.

The heater 28 is passively drainable. The heater 28 is configured toguide the fluid 25 upwardly while heating the fluid 25 and then todeliver the fluid 25 to the thermal processor 22.

With reference to FIG. 1, where the apparatus preferably is arranged ina gravitational field, the processor fluid inlets 38 are at higherelevations in the apparatus; the rundown tank 24 is lowermost; and theheater 28 and thermal processor 22 are at intermediate elevations.

The rundown tank 24 has a rundown tank fluid containing portion 41 withcapacity to hold the entire volume of fluid 25 required by theapparatus, and a gas-accommodating rundown tank headspace portion 40above the rundown tank fluid containing portion 41. The fluid 25 isshown occupying the rundown tank fluid-containing portion 41. Therundown tank headspace portion 40 is equipped with a rundown tankheadspace vent 71 providing the ability to relieve a pressuredifferential relative to the ambient environment, and with a paddingvalve 64 providing the ability to admit a padding gas to the rundowntank headspace portion 40 to relieve underpressure when air is to beexcluded. Additionally, it often is desirable to fluidly connect therundown tank headspace portion 40 with other gas-containing spaces inthe apparatus, e.g., the 32 of the thermal processor 22, to equalizepressure differentials between such spaces when one of them is fillingand another is emptying. Such structure, e.g. tubing, is explicitlydrawn and described elsewhere herein.

With continued reference to FIG. 1, in a first mode of operation,associated with the thermal processing of a process material, theapparatus transfers heat continuously from the heater 28 to the thermalprocessor 22. The pump 26 urges the fluid 25 to flow in a heat transfercirculation loop through the heater 28 and the thermal processor 22,i.e., through the heater 28, where the fluid 25 is heated, to thethermal processor 22, where the fluid 25 deposits heat, and back to theheater 28. In FIG. 1, the rundown tank 24 is drawn as being in this heattransfer circulation loop. It should be understood that a tube conveyingfluid 25 from the thermal processor 22 to the heater 28 might havesufficient capacity to be regarded as being the rundown tank 24 forpurposes of the FIRST exemplary embodiment. However, certain otherembodiments described herein will require the rundown tank 24 to beequipped with sensors and to create a fluid surface suitable forhydration.

With continued reference to FIG. 1, it also should be understood thatthe location and interconnection of the pump 26 may vary, so long as iturges the fluid 25 to travel in the heat transfer circulation loop andso long as the pump 26 drains passively when it is not activated. Inthis regard, a pump has the advantage that, properly oriented andconnected, it allows unimpeded passive drainage when it is not pumping.

The heater 28 heats the fluid 25. The fluid 25 then flows via the heateroutlet tube 80, through the heat transfer fluid inlet 38 to the heattransfer fluid spaces 32 of the thermal processor 22. Heat flows fromthe heat transfer fluid spaces 32 to the process space 34 of the thermalprocessor 22. The fluid 25 occupies the heat transfer fluid space 32 andthen flows from the heat transfer fluid space 32 via the heat transferfluid outlet 84 via the heat transfer fluid outlet drain tube 85 to therundown tank 24. While this mode of operation continues, the pump 26once again urges the fluid 25 to flow in the heat transfer circulationloop.

With continued reference to FIG. 1, in a second mode of operation, theflow of fluid 25 in the heat transfer circulation loop abruptly orunexpectedly ceases—as might occur if the pump 26 stops or the heattransfer circulation loop, heater 28, thermal processor 22, or rundowntank 24 loses integrity while fluid 25 is flowing in the apparatus (seefirst mode of operation, above), or if for any reason it is desired tostop the apparatus.

After the pump 26 has stopped, fluid 25 in the heater 28 tends to flowbackwards from the heater 28, through the pump 26, into the rundown tank24. As mentioned, the heater 28 is passively drainable: no pumping isnecessary in order for fluid 25 in the heater 28 to drain out of theheater 28.

After the pump 26 has stopped, heat transfer fluid 25 in the heateroutput tube 80 tends to flow either backward to the heater 28 or forwardinto the heat transfer fluid spaces 32 of the thermal processor 22. Inthis circumstance, fluid 25 in the heat transfer fluid spaces 32 of thethermal processor 22 tends to flow to the rundown tank 24. As mentioned,the heat transfer fluid spaces 32 are passively drainable: no pumping isnecessary in order for fluid 25 in the heat transfer fluid spaces 32 todrain out of the heat transfer fluid space 32. With particular referenceto FIG. 1, as the apparatus is drawn in this figure, the heat transferfluid 25 enters the heat transfer fluid space 32 from above and exitsthe heat transfer fluid space 32 to below. Alternatively, the relativeelevations of the heat transfer fluid inlet 38 and heat transfer fluidoutlet 84 may be approximately equal, and the fluid 25 wouldnevertheless drain from the heat transfer fluid space 32 to the rundowntank 24.

Because the heater 28 and heat transfer fluid space 32 are passivelydrainable, it is practicable to configure these structures such that, inthe event that the pump 26 abruptly or unexpectedly stops while fluid isin the heat transfer circulation loop, the fluid 25 will drain down tothe rundown tank 24 passively, rather than remaining elsewhere in theheat transfer circulation loop. Preferably, the fluid 25 that drainspassively is collected in the rundown tank 24; however, as mentionedabove, a different structure, not strictly regarded as a tank butsuitably dimensioned and equipped and located at a low elevation in theheat transfer circulation loop, may serve adequately in this FIRSTembodiment.

FIG. 2 is a schematic view of A SECOND EXEMPLARY EMBODIMENT of amolten-salt-indirectly heated screw-type thermal processing apparatus inaccordance with the present invention, shown generally at 20, having athermal processor 22 with heat transfer fluid spaces 32, heat transferfluid inlets 38, heat transfer fluid outlets 84, process space 34,conveyor 90, process material inlet 82 and process material outlet 86; arundown tank 24 with rundown tank fluid-containing portion 41(containing a fluid 25) and rundown tank headspace portion 40; a pump26, and a heater 28. The heater 28 has a heater outlet 78 and a heateroutput tube 80.

A gravity tube 204 fluidly communicates with the heat transfer fluidinlet 38 at a first height 211 and with the heater output tube 80 at asecond height 212. The second height 212 is above the first height 211.

A gravity tube upper drain 206 fluidly communicates with the gravitytube 204 at a third height 213. The third height 213 is above the secondheight 212. The gravity tube upper drain 206 also fluidly communicateswith the rundown tank headspace portion 40.

A gravity tube gas orifice 208 fluidly communicates with the gravitytube 204 at a fourth height 214. The fourth height 214 is above thethird height 213. The gravity tube gas orifice 208 fluidly communicateswith the rundown tank headspace portion 40.

A gravity tube lower drain 210 fluidly communicates with the gravitytube 204 at a fifth height 215. The fifth height 215 is below the firstheight 211. The gravity tube lower drain 210 fluidly communicates withthe rundown tank headspace portion 40 at a sixth height 216. The sixthheight 216 is below the fifth height 215.

The gravity tube 204 feeds fluid 25 to the thermal processor 22, andalso to the rundown tank headspace portion 40 via the gravity tube lowerdrain 210. The gravity tube upper drain 206 conducts excess fluid flowto the rundown tank headspace portion 40 as will be discussed in moredetail below. The gravity tube gas orifice 208 relieves pressuredifferentials should they develop between the gravity tube 204 and therundown tank headspace portion 40. The gravity tube lower drain 210provides for passive drainage from the thermal processor 22 to therundown tank 24 should fluid 25 cease to flow in the heat transfercirculation loop and, while fluid 25 is flowing, maintains enough fluidflow to avoid being obstructed by solidifying cooled fluid 25.

With regard to the thermal processor 22 as drawn in FIG. 2, notably, theheat transfer fluid inlets 38 are at elevations below the elevations ofthe respective heat transfer fluid outlets 84. The thermal processor 22has a thermal processor low portion 35 and a thermal processor highportion 37. The heat transfer fluid inlets 38 are located on the thermalprocessor low portion 35 on the conveyor 90. The heat transfer fluidoutlets 84 are located on the thermal processor 22 high portion 37 andon the conveyor 90. A fluid outlet drain tube 85 fluidly connects theheat transfer fluid outlets 84 to the rundown tank headspace portion 40.The fluid outlet drain tube 85 incorporates a vacuum breaker 92. Avacuum breaker connector tube 93 fluidly connects the vacuum breaker 92with the rundown tank headspace portion 40. The vacuum breaker 92fluidly communicates with the heat transfer fluid outlets 84 and thevacuum breaker connector tube 93 at an eighth height 218 within a rangebetween the first height 211 and the second height 212.

FIG. 2 is now referenced digressively to introduce A THIRD EXEMPLARYEMBODIMENT of a molten-salt-indirectly heated screw-type thermalprocessing apparatus in accordance with the present invention, having arestrictor 46 located in the gravity tube lower drain 210 at a seventhheight 217. The seventh height 217 is between the fifth height 215 andthe sixth height 216. The restrictor 46 has a restrictor cross-section,the heat transfer fluid outlet 84 of the thermal processor 22 has acombined heat transfer fluid outlet cross-section, and the restrictorcross-section is a predetermined fraction of the heat transfer fluidoutlet cross-section.

With continued reference to FIG. 2 and to the SECOND and THIRD exemplaryembodiments, in the previously discussed first mode of operation, withthe pump 26 activated and a body of fluid 25 provided for the system,the fluid 25 flows from the heater outlet 78, via the heater output tube80, to the gravity tube 204, where it flows downward under the influenceof gravity. A major portion of the fluid 25 passing through the gravitytube 204 flows through the heat transfer fluid inlets 38 at the thermalprocessor low portion 35, into the heat transfer fluid spaces 32, whereit fills the heat transfer fluid spaces 32 and eventually exits the heattransfer fluid outlets 84 at the thermal processor high portion 37 andflows through the fluid outlet drain tube 85 to the rundown tankheadspace portion 40. A minor portion of the fluid 25 passing throughthe gravity tube 204 passes through the restrictor 46 to the rundowntank headspace portion 40.

With continued reference to FIG. 2, in the previously discussed secondmode of operation, after the pump 26 has stopped, fluid 25 in the heateroutput tube 80 and gravity tube 204 tends to flow either backwardsthrough the heater outlet 78 into the heater 28 and from thereultimately into the rundown tank 24, or down the gravity tube 204, intothe gravity tube lower drain 210, through the restrictor 46, into therundown tank headspace portion 40. Fluid 25 in the heat transfer fluidspaces 32 tends to flow backward through heat transfer fluid inlets 38at the thermal processor low portion 35, into the gravity tube lowerdrain 210, through the restrictor 46, to the rundown tank headspaceportion 40.

With continued reference to FIG. 2, in a third mode of operation, whilethe pump 26 is active and fluid 25 is flowing in the apparatus, the rateat which fluid 25 passes from the heater output tube 80 to the gravitytube 204 exceeds the rate at which fluid 25 enters the heat transferfluid inlets 38. One way in which this could occur is for the heattransfer fluid 25 to flow slowly through heat transfer fluid spaces 32of the thermal processor 22 due to increased viscosity there during acold startup or due to some other impedance of flow. In any event, inthis third mode of operation, the fluid 25 tends to accumulate in thegravity tube 204. In this situation, it may be desirable to establishequilibrium of fluid inflow and outflow of the gravity tube 204. Forexample, it may be desirable to do so by reducing the output of the pump26 or heater 28. However, it might transpire that the pump output is notreduced or not sufficiently reduced. Alternatively, or simultaneously,it may be desirable that the fluid overflows without detriment throughgravity tube upper drain 206 at height 213. In any event, the apparatustolerates fluid 25 exiting the heater output tube 80 at a rate greaterthan the rate at which fluid 25 is entering the heat transfer fluidspace 32 of the thermal processor 22, by accommodating the excess flow.

A first means of accommodating excess flow from the heater output tube80 to the gravity tube 204 in this manner is for the gravity tube 204 tobe configured to deliver fluid 25 to the rundown tank 24 while alsodelivering fluid 25 to the heat transfer fluid space 32. As excess fluid25 accumulates in the gravity tube 204, its pressure due to gravityincreases and the combined rates at which the fluid 25 flows from thegravity tube 204 to the heat transfer fluid space 32 and from thegravity tube 204 through the gravity tube lower drain 210 through therestrictor 46 to the rundown tank headspace portion 40 may approach therate at which fluid 25 is flowing from the heater 28 to the gravity tube204. Accomplishing this simultaneous flow is one motivation theinventors had for fluidly connecting the gravity tube 204 to the rundowntank headspace portion 40 as well as to the heat transfer fluid inlets38. The restrictor 46 serves to establish the heat transfer fluid space32 of the thermal processor 22 as a favored path of flow, directing amajor portion of the fluid flow into that path, while at the same timeassuring continuous flow of a minor portion of the fluid flow throughthe restrictor 46 and into the rundown tank headspace portion 40, sothat solidification and consequent blockage do not occur there.

A second means of accommodating this excess flow from the heater 28 intothe gravity tube 204 by increasing its rate of exit from the gravitytube 204 is for the gravity tube 204 to be configured such that fluid 25passively drains to the rundown tank headspace portion 40 via yetanother path when, despite flowing both via the heat transfer fluidspaces 32 and via the gravity tube lower drain 210, the heat transferfluid 25 continues to accumulate in the gravity tube 204. To make thishappen, the gravity tube upper drain 206 fluidly connects the gravitytube 204 to the rundown tank headspace portion 40. When fluid 25 in thegravity tube 204 rises to the third height 213, the gravity tube upperdrain 206 carries excess fluid 25 directly to the rundown tank headspaceportion 40.

With continued reference to FIG. 2, in a fourth mode of operation, theapparatus is started from a rest condition in which most or all of thefluid 25 is in the rundown tank 24 and little or none of the fluid 25 isin the heater 28 or thermal processor 22. Different conditions mayprevail at such a time; they will be discussed separately in variousparts of this detailed description. Here we describe a first manner ofstarting the apparatus from such a rest condition.

The rundown tank 24 has a rundown tank fluid-containing portion 41 andthe pump 26, wherever located, is fluidly connected so as to be able tourge fluid 25 in the rundown tank fluid-containing portion 41 into andthrough the heater, wherever the heater 28 is located, and into thegravity tube 204. One suitable variety of pump 26 is a centrifugal pumphaving an impeller configured to capture fluid 25 centrally andaccelerate fluid 25 radially within a housing which directs radiallyaccelerated fluid 25 to, or draws ingestible fluid 25 from, the heater28. One suitable location for the pump 26 is at a relatively lowelevation within the rundown tank fluid-containing portion 41; anotheris outside the rundown tank 24 and connected to draw fluid 25 therefrom;another is downstream of the heater 28 and upstream of the gravity flowtube. The heater 28 may be located within the rundown tank 24, outsidethe rundown tank 24, or part inside and part outside, either upstream ordownstream of the pump. Whatever the spatial relationships between pump,heater 28 and rundown tank 24, the result is the provision of fluid 25via the heater output tube 80 to the gravity flow tube 204.

The pump 26 starts. The pump 26 causes fluid 25 to emerge from theheater outlet 78 and flow through the heater output tube 80 into thegravity tube 204. The fluid 25 enters the gravity tube 204, possiblyaccumulating in the gravity tube 204, building up pressure in thegravity tube 204. Under this pressure, the fluid 25 flows through thegravity tube 204 to the heat transfer fluid spaces 32 of the thermalprocessor 22. Heat flows from the heat transfer fluid spaces 32 to theprocess space 34. As the fluid 25 accumulates in the heat transfer fluidspaces 32, it builds up pressure there. When the fluid 25 reaches therespective heights of the heat transfer fluid outlets 84, it flows viathe fluid outlet drain tube 85 to the rundown tank 24. While this modeof operation continues, the pump 26 once again pressurizes the fluid 25and the fluid 25 once again flows to the heater 28. The heat transfercirculation loop is established.

FIG. 3 is a schematic view of A FOURTH EXEMPLARY EMBODIMENT of amolten-salt-indirectly heated screw-type thermal processing apparatus inaccordance with the present invention, shown generally at 20, havingstructure and interconnection as described for the THIRD exemplaryembodiment with reference to FIG. 2, but for the presence of a fill tank30 fluidly communicating with the gravity tube 204 at the second height212 and with the gravity tube upper drain 206 at the third height 213,and the presence of a stem pipe 48 fluidly communicating with the filltank 30 at the third height 213 and also with the gravity tube upperdrain 206 (the stem pipe 48 provides the means by which the gravity tubeupper drain 206 opens upwardly within the fill tank 30).

The apparatus of this FOURTH exemplary embodiment operates largely asdescribed for the THIRD exemplary embodiment with reference to FIG. 2,with a few exceptions. The fill tank 30 provides an increased capacity—areservoir—of fluid. The stem pipe 48 has an opening in the fill tank 30at the third height 213 and directs fluid 25 into gravity tube upperdrain 206, from which the fluid 25 flows to the rundown tank headspace40 whenever the fluid level in the fill tank 30 rises above the thirdheight 213. The gravity tube gas orifice 208 fluidly communicates withthe fill tank 30 at a higher level, which could be regarded as beingwithin a fill tank headspace portion 72—high enough that it is exposedto gas, but not to liquid, and thus remains open to relieve gas pressuredifferentials between the rundown tank headspace portion 40 and the filltank 30.

FIG. 4 is a schematic view of A FIFTH EXEMPLARY EMBODIMENT of amolten-salt-indirectly heated screw-type thermal processing apparatus inaccordance with the present invention, shown generally at 20. This FIFTHexemplary embodiment is selectively configurable to establish apreheating fluid circulation loop through the rundown tank 24 and theheater 28 and to interrupt the heat transfer circulation loop. Theapparatus has a thermal processor 22 with heat transfer fluid spaces 32,heat transfer fluid inlets 38, heat transfer fluid outlets 84, processspace 34, conveyor 90, process material inlet 82 and process materialoutlet 86; a rundown tank 24 with rundown tank fluid-containing portion41 (containing a fluid 25) and rundown tank headspace portion 40; a pump26, and a heater 28. The heater 28 has a heater outlet 78 and a heateroutput tube 80. A fill tank 30—specifically, a fill tank bottom portion36, fluidly communicates with the heater output tube 80 and with agravity tube 204 at a second height 212 and with a gravity tube upperdrain 206 at a third height 213. The fill tank 30 has a fill tankheadspace portion 72. A stem pipe 48 fluidly communicates with the filltank headspace portion 72 at the third height 213 and also fluidlycommunicates with the gravity tube upper drain 206.

The fill tank 30 provides an increased capacity—a reservoir—of fluid.The stem pipe 48 has an opening in the fill tank 30 at the third height213 and directs fluid 25 into gravity tube upper drain 206 communicatingto the rundown tank headspace 40 whenever the fluid level in the filltank 30 exceeds the third height 213. Gravity tube 204 directs fluid 25to the gravity tube lower drain 210 and to the heat transfer fluidinlets 38. The gravity tube gas orifice 208 fluidly communicates withthe fill tank headspace 72 at the fourth height 214—high enough that itis exposed to gas, but not to liquid, and thus remains open to relievegas pressure differentials between the rundown tank headspace portion 40and the fill tank 30.

The gravity tube 204 fluidly communicates with the heat transfer fluidinlets 38 at a first height 211 and with the fill tank bottom portion 36at the second height 212. The second height 212 is above the firstheight 211.

The gravity tube upper drain 206 fluidly communicates with the fill tankheadspace portion 72 at the third height 213. The third height 213 isabove the second height 212. The gravity tube upper drain 206 alsofluidly communicates with the rundown tank headspace portion 40.

A gravity tube gas orifice 208 fluidly communicates with the gravitytube 204 at a fourth height 214. The fourth height 214 is above thethird height 213. The gravity tube gas orifice 208 fluidly communicateswith the rundown tank headspace portion 40.

The gravity tube lower drain 210 fluidly communicates with the gravitytube 204 at a fifth height 215. The fifth height 215 is below the firstheight 211. The gravity tube lower drain 210 fluidly communicates withthe rundown tank headspace portion 40 at a sixth height 216. The sixthheight 216 is below the fifth height 215.

The gravity tube 204 feeds fluid 25 to the thermal processor 22 via theheat transfer fluid inlets 38 and also feeds fluid 25 to the rundowntank headspace portion 40 via the gravity tube lower drain 210. Thegravity tube upper drain 206 conducts excess fluid flow to the rundowntank headspace portion 40 as will be discussed in more detail below. Thegravity tube gas orifice 208 relieves pressure differentials should theydevelop between the fill tank 30 and the rundown tank headspace portion40. The gravity tube lower drain 210 provides for passive drainage fromthe thermal processor 22 to the rundown tank 24 should fluid 25 cease toflow in the heat transfer circulation loop and, while fluid 25 isflowing, maintains enough fluid flow to avoid being obstructed bysolidifying cooled fluid.

The heat transfer fluid inlets 38 are at elevations below those of therespective heat transfer fluid outlets 84. The thermal processor 22 hasa thermal processor low portion 35 and a thermal processor high portion37. The heat transfer fluid inlets 38 are located on the thermalprocessor 22 low portion 35. The heat transfer fluid outlets 84 arelocated on the thermal processor 22 high portion 37. A fluid outletdrain tube 85 fluidly connects the heat transfer fluid outlets 84 to therundown tank headspace portion 40. The fluid outlet drain tube 85incorporates a vacuum breaker 92. A vacuum breaker connector tube 93fluidly connects the vacuum breaker 92 with the rundown tank headspaceportion 40. The vacuum breaker 92 fluidly communicates with the heattransfer fluid outlets 84 and the vacuum breaker connector tube 93 at aneighth height 218. The eighth height 218 is above the first height 211and below the second height 212.

A restrictor 46 is located in the gravity tube lower drain 210 at aseventh height 217. The seventh height 217 is between the fifth height215 and the sixth height 216. The restrictor 46 has a restrictorcross-section, the heat transfer fluid outlet of the thermal processor22 has a heat transfer fluid outlet cross-section, and the restrictorcross-section is a predetermined fraction of the heat transfer fluidoutlet cross-section.

With continued reference to FIG. 4, in the previously discussed firstmode of operation, with the pump 26 activated and a body of fluid 25provided for the system, the fluid 25 flows from the heater outlet 78,via the heater output tube 80, to the fill tank bottom portion 36, whereit accumulates and builds pressure. Meanwhile, from the fill tank bottomportion 36, the fluid 25 flows into the gravity tube 204 and downwardtherein under the influence of gravity. A major portion of the fluid 25passing through the gravity tube 204 flows through the heat transferfluid inlets 38 at the thermal processor low portion 35, into the heattransfer fluid spaces 32, where it fills the heat transfer fluid spaces32 and eventually exits the heat transfer fluid outlets 84 at thethermal processor high portion 37, and flows through the fluid outletdrain tube 85 to the rundown tank headspace portion 40. A minor portionof the fluid 25 passing through the gravity tube 204 passes through thegravity tube lower drain 210 and the restrictor 46 to the rundown tankheadspace portion 40.

With continued reference to FIG. 4, in the previously discussed secondmode of operation, after the pump 26 has stopped, fluid 25 in the heateroutput tube 80, fill tank bottom portion 36, and gravity tube 204 tendsto flow either backwards through the heater outlet 78 into the heater 28and from there ultimately into the rundown tank 24, or down the gravitytube 204, into the gravity tube lower drain 210, through the restrictor46, into the rundown tank headspace portion 40. Fluid 25 in the heattransfer fluid spaces 32 tends to flow backward through heat transferfluid inlets 38 at the thermal processor low portion 35, into thegravity tube lower drain 210, through the restrictor 46, to the rundowntank headspace portion 40.

With continued reference to FIG. 4, in a third mode of operation, whilethe pump 26 is active and fluid 25 is flowing in the apparatus, the rateat which fluid 25 passes from the heater output tube 80 to the fill tankbottom portion 36 exceeds the rate at which fluid 25 enters the heattransfer fluid inlets 38 of the thermal processor 22. One way in whichthis could occur is for the transfer fluid 25 to flow slowly throughheat transfer fluid spaces 32 of the thermal processor 22 due toincreased viscosity there during a cold startup or due to some otherimpedance of flow. However this third mode of operation occurs, thefluid tends to accumulate in the fill tank bottom portion 36. In thissituation, it may be desirable to establish equilibrium of fluid inflowand outflow of the fill tank bottom portion 36. For example, it may bedesirable to do so by reducing the output of the pump 26 and heater 28.However, it might transpire that the pump output is not reduced or notsufficiently reduced. Alternatively, or simultaneously, it may bedesirable for fluid 25 to exit the heater output tube 80 at a rategreater than the rate at which fluid 25 is entering the heat transferfluid spaces 32 of the thermal processor 22, in which case the excessflow must be accommodated.

A first means of accommodating excess flow from the heater output tube80 to the fill tank 30 and then into the gravity tube 204 in this manneris for the gravity tube 204 to be configured to deliver fluid 25 to therundown tank 24 while also delivering fluid 25 to the heat transferfluid space 32. As excess fluid 25 accumulates in the fill tank 30, itslevel rises, its pressure increases, and the combined rates at which thefluid 25 flows from the gravity tube 204 to the heat transfer fluidspaces 32 and from the gravity tube 204 through the gravity tube lowerdrain 210 through the restrictor 46 to the rundown tank headspaceportion 40 may approach the rate at which fluid 25 is flowing from theheater 28 to the gravity tube 204. Accomplishing this simultaneous flowis one motivation the inventors had for fluidly connecting the gravitytube 204 to the rundown tank headspace portion 40 via the gravity tubelower drain 210 as well as to the thermal processor 22 via the heattransfer fluid inlets 38. The restrictor 46 serves to establish the heattransfer fluid space 32 of the thermal processor 22 as a favored path offlow, directing a major portion of the fluid flow into that path, whileat the same time allowing flow of a minor portion of the fluid flowthrough the restrictor 46 and into the rundown tank headspace portion 40as long as fluid 25 is flowing from the fill tank 30 to the gravity tube204, so that solidification and consequent blockage does not preventdrainage to the rundown tank headspace portion 40.

A second means of accommodating this excess flow from the heater 28 intothe fill tank 30 by increasing its rate of exit from the fill tank 30 isfor the fill tank 30 to be configured such that fluid 25 passivelydrains to the rundown tank headspace portion 40 via yet another pathwhen, despite flowing both via the heat transfer fluid space 32 and viathe gravity tube lower drain 210, the heat transfer fluid 25 continuesto accumulate in the fill tank 30. To make this happen, the stem pipe 48fluidly communicates with the gravity tube upper drain 206, which isfluidly connected to the rundown tank headspace portion 40. When fluid25 in the fill tank 30 rises to the third height 213, the stem pipe 48conducts excess fluid 25 into the gravity tube upper drain 206, where itflows directly to the rundown tank headspace portion 40.

With continued reference to FIG. 4, in a fourth mode of operation, theapparatus is started from a rest condition in which most or all of thefluid 25 is in the rundown tank 24 and little or none of the fluid 25 isin the heater 28, fill tank 30 or thermal processor 22. Differentconditions may prevail at such a time; they will be discussed separatelyin various parts of this detailed description. Here we describe a firstmanner of starting the apparatus from such a rest condition.

The rundown tank 24 has a rundown tank fluid-containing portion 41 andthe pump 26, wherever located, is fluidly connected so as to be able tourge fluid 25 in the rundown tank fluid-containing portion 41 into andthrough the heater 28, wherever the heater 28 is located, and into thefill tank 30. One suitable variety of pump 26 is a centrifugal pumphaving an impeller configured to capture fluid 25 centrally andaccelerate fluid 25 radially within a housing which directs radiallyaccelerated fluid 25 to, or draws ingestible fluid 25 from, the heater28. One suitable location for the pump 26 is at a relatively lowelevation within the rundown tank fluid-containing portion 41; anotheris outside the rundown tank 24 and connected to draw fluid 25 therefrom;another is downstream of the heater 28 and upstream of the fill tank 30.The heater 28 may be located within the rundown tank 24, outside therundown tank 24, or part inside and part outside, either upstream ordownstream of the pump 26. Whatever the spatial relationships betweenpump 26, heater 28 and rundown tank 24, the result is the provision offluid 25 via the heater output tube 80 to the fill tank 30 and fromthere to the gravity tube 204.

The pump 26 starts. The pump 26 causes fluid 25 to emerge from theheater outlet 78 and flow through the heater output tube 80 into thefill tank 30. The fluid 25 flows from the fill tank bottom portion 36into the gravity tube 204, building up a head of pressure in the gravitytube 204. Under this pressure, the fluid 25 flows from the gravity tube204 through the heat transfer fluid inlets 38 to the heat transfer fluidspaces 32 of the thermal processor 22. Heat flows from the heat transferfluid spaces 32 to the process space 34. As the fluid 25 accumulates inthe heat transfer fluid spaces 32, it builds up pressure there due toits depth. When the fluid 25 reaches the height of the heat transferfluid outlets 84, it flows out the heat transfer fluid outlets 84,through the fluid outlet drain tube 85, to the rundown tank 24. Whilethis mode of operation continues, the pump 26 once again pressurizes thefluid 25 and the fluid 25 once again flows to the heater 28. The heattransfer fluid circulation loop is established.

The immediately previous description of the FIFTH embodiment withreference to FIG. 4 addresses cases in which the fluid 25 already is ina condition to flow through the apparatus—i.e., cases in which the fluid25 is not too viscous to flow in a manner approximating that describedwith reference to the first mode of operation, continuous transfer ofheat. That description can be called a first manner of starting theapparatus. However, there are other situations that must be dealt with.

To address cases in which the fluid 25 must be rendered less viscous byheating in order for it to flow in a manner approximating that describedwith reference to the first mode of operation, continuous transfer ofheat, a second manner of starting the apparatus is described, accountingseparately for how to establish the described flow of fluid 25 throughthe rundown tank 24, through the pump 26, through the heater 28, throughthe fill tank 30, and through the heat transfer fluid spaces 32 of thethermal processor 22. A major portion, if not all, of the fluid 25 islocated in the rundown tank fluid-containing portion 41. The fluid 25 istoo viscous to flow efficiently through the apparatus. The fluid 25 isof a type whose viscosity decreases with increasing temperature. It isnecessary to render the fluid 25 less viscous by heating it.

The rundown tank 24 has a rundown tank headspace portion 40. The rundowntank 24 has a sump 77 that is equipped with a heat trace 66 and haspedestal 68 supporting the pump 26. The rundown tank 24 is equipped withheating elements 184. The rundown tank 24 is equipped with a reliefvalve 62 and also with a padding valve 64 that is connected to a paddinggas supply tube 182. The rundown tank 24 is equipped with a sumptemperature sensor 186, a rundown tank hydration measuring device 188,and a rundown tank temperature sensor 190. A set of hydration fluidmisting nozzles 60 is located in the rundown tank headspace portion 40and is connected to a supply of a hydration fluid.

The heater 28, as drawn in FIG. 4, is external to the rundown tank 24.The heater 28 has a heater outlet 78, a heater output tube 80, and aheater inlet 54.

The pump 26 has a pump outlet 52. A pump output tube 55 fluidly connectsthe pump outlet 52 to the heater inlet 54. A bypass valve 56 is locatedin the pump output tube 55. A bypass branch tube 58 fluidly connects thebypass valve 56 to the rundown tank headspace portion 40.

A heat trace 66 is located in the rundown tank 24. The heat trace 66warms the fluid 25 along a path, which may be called the heat tracepath, originating in the rundown tank fluid-containing portion 41 andincluding a portion thereof, proximate the pump 26, from which the pump26 may draw fluid. When the heat trace 66 is activated to heat the fluid25 along the heat trace path, the fluid 25 in the heat trace path iswarmed until it is capable of flowing into the pump 26.

The impeller of the pump 26 draws fluid 25 from the heat trace path andaccelerates the fluid 25 within the pump 26 housing. The pump 26 housingdirects the accelerated fluid 25 upward through the pump outlet 52, intoto the pump output tube 55, through the heater inlet 54. The fluid 25enters the heater 28, is heated as it moves through the heater 28, andflows from the heater 28 to the fill tank 30, thence to the thermalprocessor 22 and to the rundown tank 24, as described herein previouslywith reference to the first mode of operation.

It may be deemed necessary to warm a substantial portion of the fluid 25in the rundown tank 24 before beginning to introduce the fluid 25 to theheater 28. To accomplish this objective, the bypass valve 56 (which maybe regarded as a selector valve) is operated to allow the pump outputtube 55 to fluidly communicate with the bypass branch tube 58 and notwith the heater inlet 54. With the heat trace 66 activated, when asufficient amount of material is sufficiently warmed in the rundown tankfluid-containing portion 41 to provide fluid 25 to be circulated, thepump 26 is activated, delivering fluid 25 back to the rundown tank 24via the bypass branch tube 58. This process is continued until asufficient volume of fluid 25 is warmed in the rundown tank 24 tosupport function of the heater. Then, the bypass valve 56 is operated toallow the pump output tube 55 to fluidly communicate with the heaterinlet 54 and not with the bypass branch tube 58. With the pump 26continuing to run, the fluid 25 flows from the pump 26 to the heater 28.When such condition is reached, the heat trace 66 becomes unnecessaryand may be deactivated.

At other times, the fluid 25 must be rendered less viscous by theadmixture of another material. For such times, a third manner ofstarting the apparatus is described. Once again, as discussed above, amajor volume of the fluid 25 is located in the rundown tank 24, is tooviscous to flow efficiently through the apparatus, and is of a typewhose viscosity decreases with increasing temperature. However, in thiscase, in order to avoid thermally shocking the processor 22, it isnecessary to gradually warm the processor 22 by circulating andgradually heating the heat transfer fluid 25. With some types of heattransfer fluids, it may be that the viscosity of the fluid 25 being usedis not low enough to flow efficiently until its temperature is so highthat it could not be introduced into a cold thermal processor 22 withoutunacceptable thermal shock. Although the thermal processor 22 could beheated electrically or by other means, in some circumstances theinventors find it preferable to gradually warm the thermal processor 22by circulating a mixture of fluids through the heat transfer circulationloop including the rundown tank 24, pump 26, heater 28, fill tank 30,and thermal processor 22.

To accomplish this gradual warming of the thermal processor 22 requiresseveral considerations. First to be considered, the fluid mixture isobtained from outside or is made within the apparatus. Second to beconsidered, the fluid mixture is first circulated through the apparatusat a temperature low enough to be safely introduced into the coldthermal processor 22. Third to be considered, the fluid mixture isheated while being circulated through the apparatus. Fourth to beconsidered, when the circulating heated fluid mixture has heated thethermal processor 22 to a temperature at which the thermal processor 22can safely receive a fluid 25 at the temperature at which continuousheating is to be performed, the fluid mixture circulating in theapparatus can be replaced by the fluid 25 that accomplishes continuousheating.

First, the fluid mixture is obtained from outside or is made within thecircuit of the apparatus. Generating the fluid mixture is unnecessary ifthe fluid mixture is delivered as, for example, a hydrated saltsolution. Where the fluid mixture must be generated on-site, oneapproach to generating the fluid mixture is to mist water onto the topof a volume of hot fluid 25 (a melted salt, to be more specific) in therundown tank 24 and vent steam from the rundown tank headspace portion40 to the ambient environment. A set of water-misting nozzles 60 islocated in the rundown tank headspace portion 40. The rundown tank 24has a sump 77 that is equipped with a heat trace 66 and has pedestal 68supporting the pump 26. The rundown tank 24 is equipped with heatingelements 184. The rundown tank 24 is equipped with a relief valve 62 andalso with a padding valve 64 which is connected to a padding gas supplytube 182. The rundown tank 24 is equipped with a sump temperature sensor186, a rundown tank hydration-measuring device 188, and a rundown tanktemperature sensor 190.

When starting with solidified salt occupying the rundown tankfluid-containing portion 41, the fluid mixture is generated by heatingthe salt in the rundown tank 24 as described previously with referenceto the second manner of starting the apparatus, then slowly mistingwater onto the melted salt fluid 25 and venting excess steam from therundown tank 24 to the ambient environment while continuing torecirculate the melted salt through the rundown tank 24 via the bypassvalve 56 and the bypass branch tube 58. When the salt is sufficientlyhydrated and its temperature is low enough to be introduced safely intothe cold thermal processor 22, the nozzles 60 are deactivated, thebypass valve 56 is closed and the next step can begin, namely,circulating the fluid mixture through the heat transfer circulation loopof the apparatus.

Another approach to generating the fluid mixture is to locate an eductorin the preheating fluid circulation loop. FIG. 5, a schematicrepresentation of a SIXTH EXEMPLARY EMBODIMENT of amolten-salt-indirectly heated screw-type thermal processing apparatus inaccordance with the present invention, shown generally at 20, showsapparatus resembling the FIFTH exemplary embodiment but differing in howit provides an additive to the fluid 25. An eductor 232 is located inthe rundown tank fluid-containing portion 41 and is fluidly connected toan additive supply tube 230. The eductor 232 is immersed in or filledwith the fluid 25. The additive, e.g., water, steam or another hydratingfluid, enters from the additive supply tube 230 and mixes with the fluid25 as the fluid 25 passes through the eductor 232. As with the FIFTHexemplary embodiment, either the salt in the rundown tank 24 already ismelted, or it must be melted by heating the salt in the rundown tank 24as described previously with reference to the second manner of startingthe apparatus. Once melted salt is available, the eductor 232 isoperated and steam is vented from the rundown tank 24 to the ambientenvironment while the melted salt is recirculated to the rundown tank 24via the bypass valve 56 and bypass branch tube 58. When the salt issufficiently hydrated and its temperature is low enough to be introducedsafely into the cold thermal processor 22, the eductor 232 isdeactivated, the bypass valve 56 is closed and subsequent steps canbegin, such as circulating the fluid mixture through the heat transfercirculation loop of the apparatus, adding heat to the hydrated salt, anddehydrating the hydrated salt.

Yet another approach to generating the fluid mixture is to locate asparge tube 234 in the rundown tank fluid-containing portion 41. FIG. 6,a schematic representation of a SEVENTH EXEMPLARY EMBODIMENT of amolten-salt-indirectly heated screw-type thermal processing apparatus inaccordance with the present invention, shown generally at 20, showsapparatus resembling the SIXTH exemplary embodiment but once againdiffering in how it provides an additive to the fluid. A sparge tube 234is located in the rundown tank fluid-containing portion 41 and isfluidly connected to an additive supply tube 230. The sparge tube 234 isimmersed in the fluid. The hydration fluid enters from the additivesupply tube 230, exits the finely perforated sparge tube 234, and mixeswith the fluid in the rundown tank fluid-containing portion 41. As withthe FIFTH and SIXTH exemplary embodiments, either the salt in therundown tank 24 already is melted, or it must be melted by heating thesalt in the rundown tank 24 as described previously with reference tothe second manner of starting the apparatus. Once melted salt isavailable, the sparge tube 234 is operated and steam is vented from therundown tank 24 to the ambient environment while the melted salt isrecirculated to the rundown tank 24 via the bypass valve 56 and bypassbranch tube 58. When the salt is sufficiently hydrated and itstemperature is low enough to be introduced safely into the cold thermalprocessor 22, the sparge tube 234 is deactivated, the bypass valve 56 isclosed and subsequent steps can begin, such as circulating the fluidmixture through the heat transfer circulation loop of the apparatus,adding heat to the hydrated salt, and dehydrating the hydrated salt.

Second, the fluid mixture is circulated through the heat transfercirculation loop of the apparatus at a first temperature low enough notto damage the cold thermal processor 22. The pump 26 ingests the fluidmixture from the rundown tank 24 and propels the fluid mixture to theheater 28. The fluid mixture flows from the heater 28 to the fill tank30 and from the fill tank 30 to the heat transfer fluid spaces 32 of thethermal processor 22 and then to the rundown tank 24.

Third, the heater 28 is activated and the heat transfer fluid is heatedwhile being circulated through the apparatus. The temperature of theheat transfer fluid increases. The heat transfer fluid 25 warms thethermal processor 22. As the temperature of the heat transfer fluid 25increases, the degree of hydration decreases and steam is released.Dehydration of the fluid 25 has begun.

Fourth, dehydration of the fluid 25 continues: the fluid 25 is heatedand steam is vented until the fluid 25 is suitably dehydrated (in manysituations, anhydrous), and is further heated if necessary until itreaches a predetermined temperature at which continuous heating ofprocess material in the thermal processor 22 is to be performed. Thus,the thermal processor 22 is safely and gradually heated from ambienttemperature to operating temperature and heat shock is avoided.

An effect of heating the hydrated salt to a temperature at which itbegins to dehydrate is the evolution of steam. Steam must be vented fromthe apparatus as the body of fluid 25 is dehydrated. In one approach toventing steam, the fill tank 30 has a fill tank steam vent 73. A mixtureof partially dehydrated salt and steam exits the heater 28 and passesvia the heater output tube 80 to the fill tank bottom portion 36. In thefill tank 30, steam rises to the fill tank headspace portion 72 andexits via the fill tank steam vent 73. Alternatively or additionally,exits the fill tank headspace portion 72, via the gravity tube gasorifice 208 and passes to the rundown tank headspace portion 40, whichis vented to the ambient environment. In a fifth mode of operation, theapparatus has been operating in the first mode and now is to be shutdown in a controlled manner. The manner of shutting the apparatus downdepends largely on whether the fluid being used must be rehydrated inorder to be used again to restart the apparatus—either because the saltbeing used melts at a temperature high enough to thermally shock thethermal processor 22, or because the salt melts at a temperature higherthan ambient temperature and melting it again when restarting theapparatus would be inefficient or inconvenient.

If the fluid will be usable to restart the apparatus without hydration,then a first manner of shutting down the apparatus is usable—thisentails shutting down the input of external energy to the heater 28 andshutting down the pump 26. As discussed previously with reference to thesecond mode of operation, which includes unintentional or unexpectedinterruption of the continuous heat transfer process, the fluid 25drains passively from the heater 28, the fill tank 30 and the thermalprocessor 22, preferably into the rundown tank 24.

If the fluid will require rehydration before being used again to restartthe apparatus, a second manner of shutting down the apparatus is used,which entails interrupting input of external energy to the heater 28 andstopping the pump, so that the fluid 25 in the heat transfer circulationloop passively drains to the rundown tank 24. Next, the procedure forhydrating a melted salt occupying the rundown tank 24 is performed, withthe result that, at temperature equilibrium, the rundown tankfluid-containing portion 41 will be occupied by a hydrated salt solutionwhich is liquid at ambient temperature.

As previously described, the procedure for hydrating a melted dehydratedsalt in the rundown tank 24 entails interrupting the heat transfercirculation loop in the apparatus, establishing the preheating fluidcirculation loop (the same loop that was used for preheating in therundown tank), and then hydrating the salt. The approaches to hydratingthe salt—more generally, mixing a melting-point-reducing additive intothe salt—were discussed above and include the addition of a hydrationfluid by means of such options as misting nozzles 60, an eductor 232,and a sparge tube 234. The addition process continues until the freezingpoint of the circulating fluid 25 drops to a temperature low enough topermit circulation of the fluid 25 in the heat transfer circulation loopthe next time the apparatus is to be operated.

FIG. 7, a schematic representation of an EIGHTH EXEMPLARY EMBODIMENT ofa molten-salt-indirectly heated screw-type thermal processing apparatusin accordance with the present invention, shown generally at 20, showsapparatus resembling the FIFTH exemplary embodiment, differing chieflyin that heating is performed substantially within the rundown tank 24,rather than by an external heater (see reference number 28 in previousfigures). Externally-fed and exhausted transverse fire tubes 236 arelocated in the rundown tank fluid-containing portion 41.

In the aforementioned first mode of operation, continuous processing,the fire tubes 236 and pump 26 are activated and fluid 25 flows in theheat transfer circulation loop.

In the second mode, shutdown, the fire tubes 236 and pump 26 aredeactivated and the fluid 25 drains passively to the rundown tankfluid-containing portion 41, which in this EIGHTH embodiment includesthe fire tubes 236. Subsequent rehydration may be done if a hydratedsalt has been dehydrated during operation and it is desired to store thesalt in a hydrated form.

When the apparatus is to be started and the fluid 25 has solidified inthe rundown tank fluid-containing portion 41 and in the heater, thesolidified fluid 25 must be melted. The fire tubes 236 are activated. Assoon as a temperature measured by the rundown tank temperature sensor190 proximate the pump 26 indicates that a usable amount of material hasmelted, the pump 26 may safely be started. The bypass valve 56 isoperated to interrupt the heat transfer circulation loop and toestablish the pre preheating fluid circulation loop—in this EIGHTHexemplary embodiment, the fluid 25 enters the pump 26 from portions ofthe fire tubes 236 near the pump, exits the pump outlet 52 and flows viathe pump output tube 55 back to the rundown tank 24 via the bypassbranch tube 58. Eventually, the entire body of fluid 25 in the rundowntank 24 will melt. Alternatively, with the pump 26 in active, convectionwill eventually accomplish melting of the entire body of fluid 25.

When the apparatus is to be started and it is deemed necessary tohydrate the fluid 25 before circulating it to the thermal processor 22,the previously described steps for performing hydration are performed.With this EIGHTH exemplary embodiment, with melted salt is present inthe rundown tank 24, the pump 26 is activate, the fire tubes 236 aredeactivated, the rundown tank 24 is vented and a hydration fluid ismixed with the fluid 25. When the fluid temperature measured by therundown tank temperature sensor 190 indicates a temperature consistentwith hydration, or when the water content measured by the hydrationmeasuring device 188 indicates a predetermined acceptable water content,the bypass valve 56 is operated to interrupt the preheating fluidcirculation loop and establish the heat transfer circulation loop.Hydrated fluid 25 flows through the thermal processor 22. With the pump26 and fire tubes 236 activated and the rundown tank 24 vented, thetemperature of the fluid 25 increases gradually until the operatingtemperature is reached, at which point the apparatus is operating in thefirst mode.

A variety of hydration fluids are usable to lower the melting point of aheat transfer fluid such as a salt. These include water, steam, andhydrating solutions containing other salts or metal salts—lithium salts,for example.

The salt contemplated for an exemplary embodiment in accordance with thepresent invention can be operated at up to 800° F. without an inertblanket and at up to 1100° F. with a nitrogen gas blanket to protect itfrom atmospheric carbon dioxide. The salt is a solid below 300° F. to500° F. and must be melted prior to circulation. The salt has anadvantage of moving more heat per unit volume pumped than other heattransfer fluids.

The rundown tank 24 is located below the processor and all otherequipment, allowing gravity draining. The rundown tank 24 can be fittedinternally, externally or a combination of both, with fire tubes 236,electric heating, auxiliary heat transfer fluid tubing, thermal fluidjacketing, or steam coils to melt the salt and keep it molten for anextended time or even to be the heater. In substantially allapplications, it is necessary to locate at least one heat source in oron the rundown tank 24. Such equipment may, indeed, be used to heat thefluid 25 in the system, such that, for some applications, a heater 28located outside of the rundown tank 24 may be unnecessary.Advantageously, all pumps for moving the heat transfer fluid 25 throughthe apparatus can be located in the rundown tank 24, where they areimmersed in the fluid 25 and where a reservoir of hotter, less viscousfluid 25 is likely to be available.

In a preferred embodiment of the apparatus in accordance with thepresent invention, a turbine pump or a centrifugal pump is employed. Thedrive motor is above the rundown tank 24. When the pump 26 stops, fluid25 in the pump output tube 55 can drain backwards through the pump 26into the rundown tank 24.

The inventors evaluated many molten salts for use in accordance with thepresent invention. Two salts commonly used in heat transferapplications, both sold by Coastal Chemical Company, are HITEC® brandeutectic salt mixture and HITEC SOLAR® brand salt mixture. HITEC SOLAR®is used mostly for heat storage, because it is less costly. Both ofthese two salt products have the same heat capacity for heat transfer:approximately 4.9 to 5.75 Btu/gallon/degree ° F. See,http://www.skyscrubber.com/MSR%20%20HITEC%20Heat%20Transfer%20Salt.pdf.

HITEC® brand heat transfer salt, formerly known as “HTS,” is a eutecticmixture of potassium nitrate, sodium nitrite, and sodium nitrate. It isused as a heat transfer medium because of its low melting point of 288°F., its high heat transfer coefficient and its low cost. It can be usedwith carbon steel up to 850° F. and with 304SS above that temperature.Its viscosity at 350° F. is 10 cP and at 850° F. its viscosity is 1.4cP. It is completely chemically stable up to 850° F. From 850° F. to1000° F., it slowly degenerates over a period of years. At temperaturesabove 850° F., it should be under nitrogen gas padding to protect itfrom oxygen in the air, because oxygen will slowly oxidize the nitrite,producing a mixture with an undesirable elevated melting point. Itsthermal conductivity coefficient is 0.33 to 0.35 Btu/(hr·ft·° F.),independent of temperature. Its specific heat is 0.32 to 0.35 Btu/lb/°F. Its density varies with temperature from ˜16 lbs/gallon at ˜450° F.with 5.6 Btu/gal per ° F. to ˜14 lbs/gallon at 1000° F. with 4.9 Btu/galper ° F.

HITEC SOLAR® brand salt mixture is a higher service temperature salt. Itis a two-part mixture of sodium nitrate and potassium nitrate salts. Itis thermally equivalent to the eutectic salt but has a higher meltingpoint and service temperature. It is useful up to 1100° F. Its specificheat is 0.37 Btu/lb/° F. Its melting point is 431° F. For practicalpurposes, the temperature needs to be 500-550° F. before the salt is runthrough the apparatus. For this reason, HITEC SOLAR® brand salt mixtureis first hydrated, so that the melting point of the hydrate can allowthe molten salt hydrate to be circulated at a much lower temperature ofabout 300° F. Its coefficient of thermal conductivity is 0.31Btu/(hr·ft·° F.). Its heat transfer coefficient is 1164 Btu/h/ft² per °F. Its viscosity is 2.1 cP. Its density is about 14 to 16 lbs/ft². Itsspecific heat is up to 5.75 Btu/gal/° F. See,http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.175.2487&rep=rep1&type=pdf

Other materials are often also present in the apparatus and, when theyare, in accordance with the present invention often must be managedtoward the object of effectively filling the structures of the apparatuswith fluid, the object of effectively draining fluid 25 from thosestructures, the object of appropriately modulating pressures withinthose structures, one relative to another and collectively relative toambient pressure, and the object of preserving desirable or necessarychemical or physical properties of the fluid 25 or fluid mixture.Notably in accordance with the present invention, where the apparatus islocated on the surface of the Earth, the presence and pressure of theEarth's atmosphere and its various constituents are taken into account.Also notably in accordance with the present invention, when water isadded to a salt heat-transfer material in the apparatus, water vapor maybe generated and may require attention and management.

The fluid 25 or fluid mixture may change in properties other thantemperature and viscosity. Such other properties of the fluid 25 orfluid mixture are important in operating the apparatus in accordancewith the present invention. Notably in accordance with the presentinvention, the fluid 25 or fluid mixture expands when heated. In thecase of at least one salt used as the heat-transfer fluid 25 inaccordance with the present invention, the fluid 25 expandsapproximately 25% when heated from ambient temperature to thetemperature at which continuous heating is accomplished in theapparatus. In accordance with the present invention, fluid expansion andcontraction are accommodated toward the object of avoidingcounterproductive pressure differences between the several structures ofthe apparatus and between those structures and the ambient-pressureenvironment, and toward the object of avoiding undesired fluid flowbehavior. The management of the behavior of the heat-transfer fluid 25and other materials in the apparatus is next described.

When a portion of the fluid 25 or fluid mixture expands as it is heated,it displaces any other material with which it shares a nearby portion ofthe apparatus. Either the volume of a portion of the apparatus mustchange to accommodate such displaced material, or such other materialmust contract, or such other material must move to another portion ofthe apparatus or exit the apparatus. Where the apparatus is constructedof substantially rigid vessels and tubes, as is often the case,expansion of the apparatus is impracticable. Where the fluid 25 or fluidmixture is not elastically compressible—usually such is the case withliquids and semisolids—contraction of other portions of the fluid 25 orfluid mixture to accommodate displacement is not to be expected. Where agas shares a portion of the apparatus with the fluid 25 or fluidmixture, the displacement due to expansion of the heated fluid 25 orfluid mixture may be accommodated by compression of the gas or by othervolume-reducing phenomena such as condensation, deposition, adsorptionor chemical reaction. However, in a given application, it may be thatnone of these accommodations is practicable or preferable. Then, aportion of the fluid 25 or fluid mixture or a portion of a material withwhich the fluid 25 or fluid mixture shares the apparatus must flowwithin the apparatus or exit the apparatus to accommodate thedisplacement due to expansion. In accordance with the present invention,the apparatus is equipped to relieve pressure and to allow flow of fluid25 or fluid mixture or other materials within the apparatus and exit ofsame from the apparatus, as is now described.

With reference to FIG. 4, in an exemplary embodiment of the apparatusaccordance with the present invention, fluid 25 or fluid mixturepartially fills the rundown tank 24. Unless the rundown tank 24 isdesigned to withstand a partial vacuum relative to ambientpressure—often a design requirement that is undesirable and costly tomeet—the balance of the volume of the rundown tank 24 (this volume isknown as a headspace) is occupied by gas. As the fluid 25 or fluidmixture occupying any portion of the rundown tank 24 expands withincreasing temperature, the volume available to this gas is reduced,pressurizing the gas. The rundown tank 24 is equipped with a reliefvalve 62 fluidly communicating with the rundown tank headspace portion40. When pressure in the rundown tank headspace portion 40 exceedsambient pressure by more than a predetermined tolerable value, therelief valve 62 opens and allows gas to escape from the rundown tankheadspace portion 40. Conversely, when the fluid 25 or fluid mixturecontracts or the rundown tank headspace portion 40 pressure falls belowambient pressure by more than a predetermined tolerable value, therelief valve 62 opens and allows gas to flow into the rundown tankheadspace portion 40, reducing the pressure differential. A specificexample of a gas which may be managed in this manner is air orpreferably nitrogen, which is allowed to escape to the atmosphere orenter from the atmosphere through the relief valve 62 as needed toreduce the pressure differential.

Also with continued reference to FIG. 4, in another exemplary embodimentof the apparatus in accordance with the present invention, air isundesirable as the gas in the rundown tank headspace portion 40. Thismay be the case because, for example, a constituent of air is carbondioxide, which reacts with a salt heat-transfer fluid to produce acarbonate which undesirably elevates the melting point of the salt. Insuch an embodiment, nitrogen may be employed as a padding gas to reducepressure differentials while excluding air from the rundown tankheadspace portion 40. Rather than a relief valve 62, the rundown tank 24is equipped with a padding valve 64 connected to a nitrogen reservoir.Nitrogen is introduced to the rundown tank headspace portion 40 todisplace air. When headspace pressure is high enough or low enough,relative to ambient pressure, to require relief, the padding valve 64allows nitrogen to flow to the ambient environment or from the nitrogenreservoir as needed to reduce the pressure differential.

With continued reference to FIG. 4, in an exemplary embodiment of theapparatus in accordance with the present invention, at start-up, a gasoccupies the apparatus but for the portion of the rundown tank 24occupied by fluid. As the fluid 25 moves from the pump 26 into the pumpoutput tube 55 and enters the heater 28, the fluid 25 displaces the gasfrom the pump output tube 55, forcing the gas through the heater 28 andtoward the fill tank 30. As the fluid 25 passes through the heater 28,it expands, accelerating the rate of displacement of gas toward the filltank 30. This displaced gas moves into the fill tank 30 and, in doingso, will build pressure if not relieved. Such gas pressure could opposethe flow of fluid 25 into and through the heater 28 and into the filltank 30. To relieve this gas pressure, the fill tank headspace portion72 should be vented and, more particularly, is vented by the gravitytube gas orifice 208 via the fill tank headspace connector 75 to therundown tank headspace portion 40. Thus, gas back-pressure that mightoppose flow of fluid 25 from the pump 26 through the heater 28 to thefill tank 30 is relieved. Conversely, at shut-down or during a cessationof operation, the fill tank headspace connector 75 conducts gas from therundown tank headspace portion 40 to the fill tank headspace portion 72to relieve any partial vacuum that could oppose passive drainage offluid 25 from the fill tank 30 and heater 28 to the rundown tank 24.Pressure differentials between the rundown tank 24 and the are relievedvia the relief-pad-depad valve 64 of the rundown tank 24.

During startup of the apparatus with a hydrated heat transfer fluid 25being increased from ambient temperature to continuous heatingtemperature, water vapor leaves the fluid mixture and a substantialvolume of steam evolves there and would pressurize the apparatus andoppose flow from the heater 28 to the fill tank 30 were it not relieved.To relieve steam pressure, the fill tank 30 is equipped with a fill tanksteam vent 73, which is opened to allow the steam evolving from thefluid mixture to escape, relieving any excess steam that could opposeflow of fluid 25 from the heater 28 to the fill tank 30 oroverpressurize the apparatus.

Likewise, during shutdown of the apparatus, if water is added to a saltheat-transfer fluid 25 to produce a mixture which circulates efficientlyat temperatures between ambient temperature and continuous heatingtemperature, steam is generated. In an exemplary apparatus in accordancewith the present invention, the rundown tank 24 is equipped with a setof misting nozzles 60 located in the rundown tank headspace portion 40.When planned, intentional shutdown is desired, the feeding of processmaterial to the thermal processor 22 is interrupted and the processmaterial in the thermal processor 22 is conveyed out of the thermalprocessor 22. The supply of outside energy to the heater 28 isinterrupted. The bypass valve 56 is operated to interrupt the heattransfer circulation loop and to establish the preheating fluidcirculation loop. The pump 26 is operated. Hydration fluid is suppliedto the hydrator 60 in the rundown tank headspace portion 40 and ismisted a fine spray onto the liquid salt heat-transfer fluid 25 in therundown tank 24. An intended effect of misting the water onto the saltfluid 25 is to hydrate the salt, producing a mixture having lowviscosity at temperatures between continuous heating temperature andambient temperature. An additional effect of misting the hydration fluidonto the salt fluid 25 is the production of steam, whenever the salt isat a temperature high enough to boil the water in the rundown tank 24under the existing conditions. This steam would overpressurize therundown tank 24 were it not relieved. To prepare for the steam, thepad-depad valve 64 on the rundown tank headspace 40 is opened. With thepad-depad valve 64 open, the steam generated in the rundown tank 24escapes through the pad-depad valve 64, avoiding over pressurization ofthe apparatus. In one exemplary embodiment, misting continues until thefreezing point of the hydrated salt fluid mixture reaches 60° F. Thepad-depad valve 64 will have been closed after steam no longer needs toescape.

As so far described, the heater 28, the fill tank 30 and the heattransfer fluid space 32 of the thermal processor 22 are described aspassively drainable. The structures and interrelations rendering thesestructures and the apparatus overall passively drainable are now furtherdescribed.

With continued reference to FIG. 4, in an exemplary embodiment of theapparatus in accordance with the present invention, the rundown tank 24is configured to receive fluid 25 directly from the pump 26 at thepedestal 68 should the fluid 25 flow backward into the pump 26 from theheater 28. The rundown tank headspace portion 40 is fluidly connectedwith the gravity tube gas orifice 208 on the fill tank headspace portion72 (as will be discussed shortly). The rundown tank 24 is configured toreceive fluid 25 from the heat transfer fluid spaces 32 of the thermalprocessor 22 via the processor fluid outlet drain tube 85.

In an exemplary embodiment of the apparatus in accordance with thepresent invention, the rundown tank 24 has a sump 77 formed with apedestal 68. The pump 26 is a centrifugal-type pedestal pump 26 restingon the pedestal 68 in the sump 77. A shaft connected to a motor locatedatop the rundown tank 24 drives the pump 26. The pump 26 has no seals orcheck-valves capable of halting backward flow of material from theheater 28 through the pump 26 into the rundown tank 24. The openness ofthe pump 26 to such backward flow advantageously allows fluid 25draining from the heater 28 to flow quickly into the rundown tank 24,facilitating passive drainage of the apparatus.

In an exemplary embodiment of the apparatus in accordance with thepresent invention, the heater 28 is formed to provide a continuouslyinclined fluid flow path from the heater inlet 54 to the heater outlet78. The pump output tube 55 connects the heater inlet 54 to the pumpoutlet 52. The heater output tube 80 connects the heater outlet 78 tothe fill tank bottom portion 36. Thus, the fill tank 30 and heater 28are passively drainable to the rundown tank 24 via the pump 26 under theinfluence of gravity.

With reference to FIGS. 3-7, the fill tank 30 also is equipped with astem pipe 48 opening upwardly at a high portion of the fill tank 30 andcommunicating with the fill tank headspace portion 72. The stem pipe 48is connected to the rundown tank headspace portion 40. Fluid 25 will notflow from the fill tank 30 into the stem pipe 48 unless the level offluid 25 in the fill tank 30 exceeds the level at which the stem pipe 48opens. Thus, the level at which the stem pipe 48 opens sets the maximumdepth of fluid 25 in the fill tank 30 and, by doing so, sets an upperlimit on the range of pressures the fluid 25 flowing out of the lowportion of the fill tank 30 will exert when received at the thermalprocessor 22. As long as the level of fluid 25 in the fill tank 30 isabove the level of the gravity tube 204, fluid 25 will tend to flow outof the fill tank 30, through the gravity tube 204, and through both therestrictor 46 and the thermal processor 22 to the rundown tank 24. Whenthe pump 26 ceases to drive fluid 25 up through the heater 28, fluid 25flows back rapidly from the fill tank bottom portion 36, through theheater output tube 80, through the heater 28 and pump output tube 55 tothe rundown tank 24 and, simultaneously, more slowly through the gravitytube 204 through the restrictor 46 to the rundown tank 24.

With continued reference to FIG. 4, the thermal processor 22 is nowdiscussed, first with attention to how it is interrelated with the filltank 30, the restrictor 46 and the rundown tank 24; second, withattention to how it is formed and configured to be completely fillableand passively drainable; third, with attention to how the thermalprocessor 22, restrictor 46 and fill tank 30 cooperate to accomplish theimportant object of managing fluid 25 flow during startup of theapparatus.

The thermal processor 22 has at least one thermal processor low portion35 with at least one heat transfer fluid inlet 38 and at least onethermal processor high portion 37 with at least one heat transfer fluidoutlet 84. The thermal processor 22 has at least one heat transfer fluidspace 32 fluidly communicating with the transfer fluid inlet 38 andtransfer fluid outlet 84, and has a process space 34 with processmaterial inlet 82 proximate the thermal processor low portion andprocess material outlet 86 proximate the thermal processor high portion.In some embodiments, the heat transfer fluid space 32 is inclined. Aconveyor 90 is disposed within the process space 34 and is driven by amover associated with the thermal processor 22. When the thermalprocessor 22 is at a processing temperature, process material isreceived at the process material inlet 82. The conveyor 90 is activatedand urges the process material toward the process material outlet 86.

The thermal processor 22 may require the input of a substantial amountof heat in order to reach operating temperature. Thus, in operating theapparatus in accordance with the present invention, it is observed thatduring startup the rise in temperature of the fluid 25 in the heattransfer fluid space 32 of the thermal processor 22 lags the rise intemperature of the fluid 25 flowing through the restrictor 46 to therundown tank headspace portion 40. Thus, the fluid 25 in the heattransfer fluid space 32, being cooler, is more viscous and flows moreslowly. Consequently, during startup, the total flow of fluid 25 out ofthe low portion of the fill tank 30 is reduced. However, there might notbe any mechanism in place to adjust the output of the pump 26 and heater28 to account for this reduced flow. With the pump 26 and heater 28delivering fluid 25 at a rate higher than the restrictor 46 and thethermal processor 22 together can accept fluid, the fluid 25 begins toaccumulate in the fill tank 30 (e.g., FOURTH exemplary embodiment) orgravity tube 204 (e.g., THIRD exemplary embodiment). As the level of thefluid 25 in the fill tank 30 rises, the fluid 25 pressure increases atthe restrictor 46 and at the heat transfer fluid inlet 38, increasingthe rate of flow through these two structures somewhat. This increase offlow rate might suffice to manage the excess.

If the flow from the heater 28 into the fill tank 30 (or gravity tube204, THIRD exemplary embodiment) continues to exceed the flow out fromthe fill tank 30, the level of fluid 25 in the fill tank 30 rises untilfluid 25 begins to flow through the stem pipe 48 (or gravity tube upperdrain 206, THIRD exemplary embodiment) to the rundown tank headspaceportion 40, limiting any further increase in pressure at the restrictor46 and the heat transfer fluid inlets 38, even if the pump 26 and heater28 continue to deliver fluid 25 to the fill tank 30 (or gravity tube204) at an excessive rate.

As the thermal processor 22 warms up, the fluid 25 in the transfer fluid25 flows more easily and equilibrium may be achieved with the fluidlevel stabilized at a level intermediate that of the low portion of thefill tank 30 and that of the stem pipe 48 orifice. In any event, therestrictor 46 and thermal processor 22 are never exposed to a fluidpressure greater than can be exerted by a column of fluid 25 extendingbetween the height of the heat transfer fluid 25 inlet and the height ofthe stem pipe 48 in the fill tank 30 (or the height at which the gravitytube 204 fluidly communicates with the gravity tube upper drain 206).

In accordance with the present invention, when molten salt is used as aheat transfer fluid, materials for surfaces in contact with the salt areselected based on temperature tolerance and the ability to withstandcorrosion. Carbon steel is usable for temperatures up to 800° F., 304 SSfor temperatures up to 1000° F., and 347, among other SS fortemperatures above 1000° F.

Piping and vessels are insulated to conserve heat.

The rundown tank 24 is at the lowest elevation in the system. Thehighest fill level of the rundown tank 24 is at a lower elevation thanthe thermal processor 22, fill tank 30 and heater 28. The rundown tank24 has sufficient capacity to hold 100% of the volume of heat transferfluid 25 contained by the apparatus, plus an additional 30% forexpansion and an additional 20% for safety. It is common for a preferredembodiment of the apparatus in accordance with the present invention tohave a minimum of a 150 gallon rundown tank 24 with an approximatediameter of 36 inches and an approximate length of 48″ with a sump 77projecting approximately 12 inches downward.

The pump 26 for a preferred embodiment of the apparatus in accordancewith the present invention is a pump designed for the intendedtemperature range. The pump 26 has a pump curve specific to the requiredpressure determined by the head pressure for a given installation, i.e.,pressure sufficient to deliver fluid 25 through the heater 28 to thefill tank 30 at a sufficient rate to keep the fill tank 30 at a desiredfill level. A preferred pump configuration uses a vertical shaft pitpump without a seal. The drive is above the rundown tank 24.

The fill tank bottom portion 36 is at an elevation higher than theelevation of the heat transfer fluid inlet 38 of the thermal processor22 and higher than the elevation of the rundown tank 24. The fill tank30 has a volume of approximately 5% of the volume of heat transfer fluid25 needed to run the apparatus during operation. In a preferredembodiment, the tank has a volume of about 6 gallons, although a muchlarger fill tank 30 may be more practical in some circumstances.

In a preferred embodiment of the apparatus in accordance with thepresent invention, the thermal processor 22 has a length of 26 feet, awidth of 4 feet, a height of 4 feet, with conveying screws 20 feet inlength and 14 inches in diameter. Material thicknesses are approximately5/16 inch.

In a preferred embodiment of the apparatus in accordance with thepresent invention, the heater 28 is about 4 feet in diameter and 7 feetin height.

In some embodiments, the rundown tank 24 has a rupture disk (see 192 inFIG. 4) for safe rapid release of vapor in the event of grossoverpressurization.

The tubing in which the heat transfer fluid 25 circulates is constructedof materials capable of tolerating the anticipated temperatures,pressures and chemical conditions. 347 SS is a preferred material forhigh temperatures and can be used when, as is described herein, the useof a pressure boundary material is not required for safety orcertification.

The rundown tank 24 has capacity for a volume of the heat transfer fluid25 sufficient to operate the apparatus, capacity for expansion of thefluid 25 volume, and capacity for a volume of gas above the fluid 25volume. With reference to FIG. 4, in the FIFTH exemplary embodiment,when the rundown tank 24 is occupied by a volume of fluid, it disposesthe fluid volume so as to provide a fluid upper surface 240 at a fluidupper surface height below the top of the rundown tank 24, i.e.,allowing vacant space accounted for by the rundown tank headspaceportion 40. Capacity for the volume of fluid 25 (i.e., liquefied heattransfer fluid) sufficient to operate the apparatus is important,because the entire volume of thermal transfer fluid 25 in the apparatusshould be able to drain into the rundown tank 24 when it is not beingheated and circulated, thereby avoiding retention of fluid 25 in thethermal processor 22 or elsewhere outside the rundown tank 24 whentemperatures fall below the melting point of the fluid. Capacity forexpansion of the fluid 25 is important, because the fluid 25 expands upto 25% over the range of temperatures at which it is used. Capacity fora volume of gas above the fluid 25 is important for accommodating theexpansion of the fluid 25 during heating, for accommodating the steamgenerated both during hydration and during dehydration, and forequalizing pressure differentials relative to the transfer fluid space32 of the thermal processor 22 and the fill tank headspace 72. Thedisplacement of a gas is important in managing a liquid or solid whichis in contact with the gas while managing the pressure within a portionof the apparatus relative to the environment. A fluid upper surface 240of the volume of fluid 25 is important, because it is preferable for thepump 26 to ingest the fluid 25 at a location below the fluid uppersurface 240 and because the fluid upper surface 240 creates a liquid-gasinterface at which material and heat are transferrable.

With reference to FIG. 4 and the FIFTH exemplary embodiment, the gravitytube 204 accepts heat transfer fluid 25 from the heater outlet 78 andfeeds the fluid 25 to the processor fluid inlet 38 under the influenceof gravity at a pressure determined largely by the height differentialbetween the first height 211 and the second height 212, and notdetermined by the pressure or flow rate of the pump 26. Passivelylimiting pressure to within a predetermined range in this manner isadvantageous for its simplicity and reliability. The gravity tube upperdrain 206 receives the fluid 25 flow, if any, that exceeds the fluid 25flow entering the gravity tube 204 and flowing toward the processorfluid 25 inlet 38. The gravity tube gas orifice 208 admits gas to thegravity tube 204 at times when a partial vacuum might develop in thegravity tube 204, e.g., when fluid 25 is entering the gravity tube 204from the heater outlet 78 more slowly than it is flowing into thegravity tube 204 toward the processor fluid 25 inlet 38. Conversely, thegravity tube gas orifice 208 allows gas to escape the gravity tube 204when a vapor lock might develop there, e.g., when fluid 25 is enteringthe gravity tube 204 from the heater outlet 78 more rapidly than it isflowing into the gravity tube 204 toward the processor fluid 25 inlet38. This arrangement facilitates and assures passive drainage when thepump 26 stops.

Because the processor fluid 25 outlet 84, the gravity tube 204 and thegravity tube upper drain 206 fluidly communicate with the rundown tank24, fluid 25 from these three paths converges and can again becirculated to the gravity tube 204 via the heater 28. Because thegravity tube gas orifice 208 and the vacuum breaker connector tube 93fluidly communicate with the rundown tank 24, gas is transferrable amongthe rundown tank 24, the thermal processor 22, and the gravity tube 204(portion thereof proximate heater output tube 80) or fill tank headspaceportion 72. Gas transfer is important, because the entry of thermaltransfer fluid 25 into any one of these three structures may befacilitated by allowing the gas that the fluid 25 displaces to pass toanother of these three structures. Additionally, temperature changesoften produce expansion or contraction of the heat transfer fluid 25 orof a gas, requiring gas transfer to avoid creating a troublesome ordangerous local overpressure or partial vacuum.

In an exemplary embodiment, the first height 211 and the second height212 are selected such that a column of the fluid 25 extending verticallyfrom the first height 211 to the second height 212 exerts pressure atthe processor fluid 25 inlet 38 no greater than 14.9 PSIG. Whenpressures are kept at or below this limit, structural loads and rupturehazards are mitigated and engineering standards calling for costly ASMEpressure boundary materials and construction are not implicated. As anadditional benefit, 347 SS, which is not an ASME-recognized pressureboundary material, is preferred in the construction of some embodimentsof the apparatus in accordance with the present invention.

In an exemplary embodiment, the rundown tank 24 is equipped to vent agas to the ambient environment and to receive a gas from a sourceselected from among the ambient environment of the apparatus and apadding gas supply tube 182. This arrangement, commonly a pad-depadvalve 64 fluidly connected with a supply of inert padding gas such asnitrogen, allows overpressure in the rundown tank 24 to be vented to theatmosphere and compensates for under pressure in the rundown tank 24 byadmitting inert gas to the rundown tank headspace portion 40.

The fill tank 30 (or the fluid communication of the gravity tube 204with the heater output tube) is located uppermost in the apparatus. Heattransfer fluid 25 passing from the heater outlet 78 to the fill tankbottom portion 36 at the second height 212 is free to enter the gravitytube 204 and flow downward toward the processor fluid inlets 38. Heattransfer fluid 25 which has accumulated in the fill tank 30 and hasrisen to the third height 213 in the fill tank headspace portion 72 (orin the gravity tube 204, see THIRD exemplary embodiment) enters the stempipe 48 ((e.g., FOURTH exemplary embodiment) and flows down the gravitytube upper drain 206 toward the rundown tank 24.

With reference to FIG. 4, in an exemplary embodiment, the rundown tank24 disposes the fluid volume so as to provide a fluid upper surface 240at least a portion of which is accessible and suitable for hydration.The rundown tank 24 has hydration water-dispensing nozzles 60 and arundown tank headspace vent 71. Preferably, the hydrationwater-dispensing nozzles 60 are configured to deposit a water mistgently onto the fluid upper surface 240 without disrupting it. The fluidupper surface 240 should be large enough to permit the hydration nozzles60 to efficiently add water to a body of dehydrated salt in the rundowntank 24. It is usually undesirable to cause a molten salt to erupt andsplatter in the rundown tank 24. Therefore, when hydrating hot moltensalt, the hydration water nozzles 60 should apply water in such a mannerthat the water absorbs heat from the hot salt, the water and the saltcombine to form hydrated salt, and yet the water is never injected intothe salt in a manner that could cause water to flash beneath the fluidupper surface 240. Preferably, a fine mist of water is injected abovethe salt and gently and uniformly settles onto the fluid upper surface240, whereupon some of the water vaporizes and some of the watercombines with salt. Initially, flash steam may require an efficient pathto the environment, such as may be provided by an amply dimensionedpad-depad valve 64 on the rundown tank headspace portion 40. Gradually,as the volume of hot dehydrated salt is replaced by a volume of coolerhydrated salt, the temperature and pressure in the rundown tank 24 willdecrease, at which time padding gas may be admitted through thepad-depad valve 64 to compensate for any underpressure as the remainingsteam condenses.

In an exemplary embodiment, the rundown tank 24 is equipped to heat thefluid 25 and the pump 26 and the rundown tank 24 are configuredselectively to circulate the fluid 25 between the pump 26 and therundown tank 24. When solidified salt occupies the rundown tank 24, thesalt must be liquefied in order for it to circulate. Whether coldsolidified salt is warmed in order to liquefy it, or it is hydrated inorder to produce a hydrated salt liquid (which is later dehydrated), itis preferable initially to circulate the salt in a short loop includingthe rundown tank 24 and the pump 26. In one embodiment, see FIG. 4, abypass branch 58 fluidly connects the pump 26 output to the rundown tank24 at a level above the fluid-gas boundary of the fluid upper surface240, allowing fluid 25 to flow over and through the solid salt towardthe pump 26 in the rundown tank 24. During this period, it may bepreferable to equip the rundown tank 24 with a heating element 184 whichis activated to begin liquefying the salt. The pump 26 may be positionedin a sump 77 in the rundown tank 24, in which case a heat trace 66 isinstalled on the sump 77 and is activated at this time. After asufficient amount of salt is liquefied, the heat trace 66 or heatingelement 184 is deactivated and the fluid 25 is routed to the heater 28for circulation through the apparatus.

In the exemplary embodiments of FIGS. 2-7, for example, a restrictor 46is located in the gravity tube lower drain 210 at a seventh height 217below the first height 211 and above the six height. The restrictor 46allows a minor portion, such as 2-4%, of the fluid 25 flowing into thegravity tube 204 to flow to the rundown tank 24, while a major portionflows to the thermal processor 22 fluid 25 inlet. While the pump 26 isactive, the major portion of the fluid 25 flow serves to transfer heatto the thermal processor 22, while the minor portion of the fluid 25flow serves to keep the gravity tube 204 hot so that the gravity tube204 remains capable of carrying fluid 25 to the rundown tank 24. Whenthe pump 26 is inactive or for any other reason fluid 25 is no longerbeing delivered at sufficient rate to cause it to flow through thethermal processor 22, the fluid 25 is free to flow out of the thermalprocessor 22 through the processor fluid 25 inlet 38, back to thegravity tube 204, and through the restrictor 46 214 to the rundown tank24.

In an exemplary embodiment, the heat transfer fluid outlet 84 of thethermal processor 22 is located above the first height 211. When thepump 26 stops, fluid 25 in the thermal processor 22 flows out throughthe processor fluid 25 inlet 38 and ultimately to the rundown tank 24,while fluid 25 which has left via the processor fluid 25 outlet 84 alsoflows to the rundown tank 24.

With reference to FIG. 4, an exemplary method of operating afluid-heated indirect thermal processing apparatus in accordance withthe present invention is described for use with a salt having a meltingpoint below 300° F. This method is carried out in a closed loop thermalheating system with nitrogen padding with equipment designed toaccommodate differential thermal expansion of the housing and screwconveyor. As its thermal fluid 25 heat transfer fluid, this method usesa molten salt. This exemplary method is accomplished without hydratingthe salt. As previously described with reference to the apparatus ofFIG. 4, a rundown tank 24 is located at a low point of the apparatus tofacilitate gravity draining of the thermal fluid 25 into the rundowntank 24 during shutdown. The rundown tank headspace portion 40 isnitrogen padded—i.e., nitrogen blanketed—to protect the thermal fluid25—in this exemplary method, a molten salt—from the atmosphere and tobalance the headspace pressures (in the rundown tank 24, thermalprocessor 22, heater 28 and fill tank 30) throughout the apparatus. Therundown tank 24 serves as a container for the inventory of thermal fluid25, an expansion tank as the thermal fluid 25 heats, as a receiver forthe return flow from the thermal processor 22, as a common headspace forpressure compensation, as a sump for drain-down at time of shutdown orat time of plant failure such as a power failure and as a surface forhydration/dehydration when that is advisable. The pad-depad valve 64releases air or padding gas (nitrogen, in this exemplary method) fromthe system as pressure increases due to expansion of the molten saltwhen heated. During shutdown when the molten salt cools/solidifies, thepad-depad valve 64 admits nitrogen from a nitrogen supply, filling therundown tank headspace 40 with nitrogen. The rundown tank 24 contains apump 26 which is submerged in the rundown tank 24 and is located on apedestal 68 in a sump 77 located at a low point of the rundown tank 24.The pump 26 is employed to circulate the thermal fluid 25 through theapparatus. The sump 77 has an electrical heat trace 66. Alternately,preferably additionally, the rundown tank 24 is equipped with submersionheating elements 184.

During startup, if the salt is solidified in the rundown tank 24, theheat trace 66 or heating elements 184 are activated to melt the saltaround the pump 26 and the heating elements 184 melt the salt in therundown tank 24. A flow path is created in the rundown tank 24 into thesump 77. During a cold startup, the path from the pump outlet 52 to theheater inlet 54 is closed and the bypass branch tube 58 from the pumpoutput back to the rundown tank 24 is open. Once the salt is heated tomelting around the pump 26, as detected by a temperature sensor in thesump 77, the pump motor can be started. The pump motor can be variablefrequency controlled and typically is operated at a low flow rate, withthe melting salt circulating from the sump 77, through the pump 26,through the bypass branch 58, into the rundown tank headspace portion40, and down through the flow paths created by the heating elements 184,where it returns to the sump 77 for recirculation. When the salt in therundown tank 24 is fully melted, as detected by a temperature sensor inthe rundown tank 24, the path from the pump outlet 52 to the heaterinlet 54 is opened and the bypass branch 58 is closed.

Molten salt rises from the pump outlet 52 to the heater inlet 54 andinto the bottom of the thermal fluid heater 28. The heater 28 preferablyis formed to provide a continuously inclined fluid flow path from theheater inlet 54 to the heater outlet 78 without valves in the thermalfluid loop. Valves can be used, but in this method are not required. Thethermal fluid characteristics of density and viscosity changesignificantly as the thermal fluid 25 is heated. The density andviscosity of molten salt change dramatically with temperature.Therefore, for a particular pump 26, the flow rate changes at differentoperating temperatures. In the embodiment utilized for this method, theflow rate is always more than the required by the thermal processor 22.Having reached a desired temperature in the heater 28, the molten saltexits through the heater outlet 78 located at the top of the heater 28and flows into the fill tank 30.

The fill tank 30 is located at the highest point in the apparatus andsets the head pressure on the fluid flow into the thermal processor 22.As the fill tank 30 fills with molten salt, the fill tank headspaceconnector 75 allows the air or nitrogen inside the fill tank 30 to bedisplaced into the rundown tank headspace portion 40. The salt exits thefill tank bottom portion 36 through the fill tank gravity flow tube 42and then through the thermal processor 22 branch tube 44 to the thermalprocessor 22. As mentioned previously, the flow rate of molten salt fromthe heater 28 exceeds the flow requirements of the thermal processor 22.Consequently, the level of the molten salt in the fill tank 30 rises. Astem pipe 48 inside the fill tank 30 sets the maximum fill level of thetank. The balance of excess flow discharges into the rundown tankheadspace portion 40 after entering the stem pipe 48.

The thermal processor 22 in this embodiment is a heat exchanger thattransfers heat from the thermal fluid 25 to the feed passing through thethermal processor 22. The thermal processor 22 can be one of severaldifferent types. In the thermal processor 22s used in accordance withthis exemplary method, the supply of heated thermal fluid 25 enters thethermal processor 22 at a low portion thereof and generally flows upthrough the flow paths of the processor 22 and exits a high portion.Thus, if the supply of thermal fluid 25 is cut off, the flow reversesunder the influence of gravity and exits the processor 22 at the lowportion. The thermal fluid 25 is allowed to gravity drain back to therundown tank 24 when the pump 26 shuts off. With the pump 26 operating,thermal fluid 25 exists the heat transfer fluid outlet 84 and flows to avacuum breaker 92.

The vacuum breaker connector tube 93 fluidly connects the vacuum breaker92 to the rundown tank headspace portion 40. This prevents air-lockingon startup or (vacuum-locking) during drain down by venting the gases inthe flow paths of the thermal processor 22 to the rundown tank headspaceportion 40. Thermal fluid 25 returns to the rundown tank 24 from thevacuum breaker 92 and is recirculated by the pump 26.

Another feature of this apparatus is the ability to passively limit thepressure on the fluid 25 to a few psi and therefore not requiring theheat exchanger or any of the tanks to be an ASME pressure vessel. Thisis particularly important in extremely high temperature applicationswhere the use of molten salt as the heat exchange media is employed. Thepreferred metallurgy for the salt, a commercial heat transfer salt, at1100° F. is 347SS, which is not an ASME-recognized pressure boundarymaterial.

An important design feature of all piping and equipment for the use ofmolten salt as the heat transfer fluid 25 is the gravity draining duringshutdown and when the pump 26 stops. Because the two most common moltensalts used for heat transfer fluids, HITEC® and SOLAR SALT®, freeze at288° F. and 448° F. respectively, it is necessary to drain all of theequipment and piping dry of molten salt on shutdown or power failure.During a shutdown of the system, the molten salt drains by gravity downto the rundown tank 24. Molten salt gravity drains from the fill tank30, both back to the heater 28 (and from there back through the pump 26)and also through the gravity tube 204, to the rundown tank 24. As thelines drain, the vent line to the rundown tank headspace portion 40supplies nitrogen from the padding system to fill the void created bythe draining thermal fluid. The flow from the heater 28 drains downthrough the pump 26 to the rundown tank 24. The transfer fluid spaces 32of the thermal processor 22 are self-draining to the rundown tank 24.The apparatus passively drains when the pump 26 is not operating.

Occupying relative high points of the apparatus are the fluidcommunication of the gravity tube 204 with the heater output tube 80,gravity tube upper drain 206 and gravity tube gas orifice 208 (see FIG.2), the fill tank 30 (FIGS. 3-7), and the vacuum breaker 92 (FIGS. 2-7).The gravity tube gas orifice 208 and the vacuum breaker connector tube93 gravity tube lower drain 210 are both fluidly connected to therundown tank headspace portion 40. This is important, because onshutdown, all the heat transfer fluid flow paths empty and fill with airor padding gas, which must be displaced at startup.

For molten salts with melting temperatures greater than 300° F., themolten salt must be hydrated during startup to avoid thermally shockingthe apparatus. The two major HTF salts, HITEC® and SOLAR SALT®, melt at288° F. and 448° F. respectively. Damage to the equipment could occur ifhot (>300° F.) molten salt were circulated through a cold system. It isnecessary to warm the system gradually. In the event that a salt is usedwith a melt temperature above 300° F., the salt must be hydrated duringeach startup and dehydrated during each shutdown. The process ofhydrating the salt involves adding water to the salt as it cools untilit becomes a saturated salt solution that remains in the liquid state.During startup the water is boiled out of the solution.

The primary differences between this exemplary method and the methodwithout hydration are the addition of a salt hydration system and a ventto remove the steam during dehydration. All other aspects arefundamentally the same and should be inferred from the previousdescription of a method without hydration. The following method will beemployed during each startup and shutdown to hydrate and dehydrate thesalt solution.

Hydrated salt can be already liquid at ambient temperature. It may beonly partially hydrated, which lowers the melting point, in which caseonly a slight heating can easily melt the solid. To start the apparatuswith liquid hydrated salt, the pump 26 is turned on and hydrated salt iscirculated through the system. The heater 28 is activated and the saltis heated at ramp rate of approximately 5° F. per minute to 215° F.-220°F. At this temperature, the salt will begin to dehydrate, releasingevaporated water. Depending on the volume of molten salt in the system,the temperature can be held at 220° F. until the rate of steam releasebegins to subside, or a new ramp rate of 2° F. per min can be imposedimmediately after reaching 220° F. The steam in the fill tank 30 exitsthrough a rundown tank headspace vent 71 that is open during thestartup. Steam from the thermal processor 22 vents to the rundown tank24 and vents to the rundown tank headspace vent 71, out to theenvironment. At 480° F., the molten salt eutectic becomes anhydrous andthe heating ramp rate can be set to 5° F. per minute until the finaldesired temperature has been reached. The Solar salt requires more than600 F for full dehydration.

During shutdown, the salt must be hydrated if solidification is to beprevented when it cools. At least partial hydration is required ifcirculation of the salt is to begin after melting without first havingto heat the salt to too high a temperature to begin circulation withoutunacceptable thermal shock. The heater 28 is deactivated and circulationof the salt is continued for hydration during shut down. Meanwhile, feedis emptied from the process space 34 of the processor 22. When themolten salt has cooled to near its melting temperature, the pad-depadvalve 64 is opened to the atmosphere for venting of water vapor.Hydration fluid is misted onto the top of the melted salt in the rundowntank 24 via the water misting nozzles 60. The salt is hydrated until itsfreezing point drops preferably to below 60° F. Once the salt has becomefully hydrated, the system functions in the manner of the methoddescribed above without hydration, except that the rundown tank remainsvented for dehydration up to at least 600° F.; beginning at thattemperature, the system is operated as a blanketed closed system.

To start the apparatus with solidified salt, a portion of the saltaround the pump must be melted. The melting salt expands. Provision ismade for the electric or other heat sources to melt a vertical passageto the surface of the solidified salt for the expanding liquid. Once asufficient volume of liquid is melted the pump can be started. Therundown tank 24 is an insulated tank of sufficient volume to contain thewhole volume of salt in the apparatus with room for expansion on heatingand an adequate surface area for hydration. The rundown tank headspaceportion 40 is connected to all headspaces (fill tank 30, heater 28, andprocessor 22) within the molten salt loop to maintain a common pressureand inert atmosphere and to break any siphon effects. The rundown tank24 includes a sump 77 with a heat trace 66 which the pump 26 sits in.The pump 26 is VFD driven, capable of sufficient pressure to circulatethe salt through the system. In the event the salt solidifies, the heattrace 66 melts the salt around the pump 26 and the heating elements 184melt the salt in the rundown tank 24. Alternatively, steam or thermaloil could be circulated through tubes in the rundown tank 24 as a meansof heating the salt. As the salt melts, the heating elements 184 providevertical and horizontal melt channels communicating with the sump 77 sothat molten salt can flow up to the surface of the salt in the rundowntank 24 and back to the pump 26. The pump 26 is started with the bypassvalve 56 operated so that the bypass branch 58 open. The molten salt isrecirculated into the rundown tank 24. The molten salt continuouslyexpands the molten volume by convection until the whole mass of salt inthe rundown tank 24 is melted. Once the salt is sufficiently melted, asdetected by a temperature sensor, with the mass reaching approximately480° F., the hydration of the salt can begin. The misting nozzles 60 areactivated. The hot molten salt is circulated in the rundown tank 24while hydration fluid is added. Some of the hydration fluid is absorbedby the salt, while some vaporizes. Steam vents through the pad-depadvalve 64 to the atmosphere. A rupture disk 192 protects the rundown tank24 from any gross over pressurization. As the temperature of the saltcools due to the addition of water, the salt absorbs water more rapidly.Once the salt is adequately hydrated by being a liquid at a safetemperature for starting circulation without unacceptable thermal shockto the thermal processor 22, the hydration fluid supply is turned off.At this point, a startup with hydrated salt can commence.

With reference to FIG. 1, a FIRST exemplary method of operating amolten-salt-indirectly heated screw-type thermal processor in accordancewith the present invention is carried out with a molten-salt-indirectlyheated screw-type thermal processor 22 which has an operating heattransfer fluid 25 temperature range, an operating heat transfer fluid 25flow rate range and an operating heat transfer fluid 25 pressure range.A heater, and a rundown tank are operatively connected to the thermalprocessor 22 as previously discussed.

With continued reference to FIG. 1, a heat transfer fluid 25 isprovided. The fluid 25 is capable of conveying heat from the heater 28to the thermal processor 22 at a temperature within the processor'soperating heat transfer fluid 25 temperature range while flowing intothe thermal processor 22 at a heat transfer fluid 25 flow rate withinthe processor's operating heat transfer fluid 25 flow rate range at apressure within the processor's operating heat transfer fluid 25pressure range. The volume of fluid 25 that is provided is at leastsufficient to operate with the heater 28 and thermal processor 22. Theheater 28 is capable of heating the heat transfer fluid 25 sufficientlyat the aforementioned flow rate and temperature. The rundown tank 24 hascapacity more than sufficient to contain all of the heat transfer fluid25 that is added. The pump 26 is activated and delivers the heattransfer fluid 25 from the heater 28 to the thermal processor 22 at thetemperature, the flow rate and the pressure while delivering the heattransfer fluid 25 from the thermal processor 22 to the heater. When itis desired to cease processing, the pump 26 is stopped. The heattransfer fluid 25 flows passively into in the rundown tank 24.

With reference to FIG. 4, a SECOND exemplary method of operating amolten-salt-indirectly heated screw-type thermal processor in accordancewith the present invention is carried out by using one or more heatersto produce the heat transfer fluid 25 by melting a solid. A solidmaterial such as a salt is located in the rundown tank 24. A smallportion of the material is heated until it melts, making fluid 25available to the pump. The heat transfer 25 circulation loop isinterrupted. The preheating circulation loop is established. The pump 26is activated. When a rundown tank temperature sensor indicates that thebody of salt in the rundown tank 24 has melted, the preheatingcirculation loop is interrupted and the processing circulation loop isestablished.

It is often advantageous to begin circulating a fully hydrated salt inthe heat transfer 25 circulation loop and at least partially dehydratethe salt while circulating it. With reference to FIG. 4, a THIRDexemplary method of operating a molten-salt-indirectly heated screw-typethermal processor in accordance with the present invention is carriedout with a heat transfer fluid 25 comprising a hydrating fluid. Such amethod is useful when a cold thermal processor must be protected fromsudden exposure to a very hot heat transfer fluid. With the heattransfer 25 circulation loop established, the pump 26 activated and therundown tank 24 vented, the heater 28 is activated, gradually warmingand dehydrating the fluid 25 as the fluid 25 gradually warms the thermalprocessor 22. Simultaneously dehydrating the salt and delivering thesalt to the thermal processor 22 has the advantage of gradual change ofprocessor temperature and gradual removal of water (vented as steam). Athermal processor 22 has a predetermined maximum tolerable rate oftemperature increase, the step of dehydrating is performed slowly enoughthat the thermal processor 22 is warmed at a rate no greater than thatmaximum tolerable rate.

With reference to FIG. 4, a FOURTH exemplary method of operating amolten-salt-indirectly heated screw-type thermal processor in accordancewith the present invention entails making the melting-point-reducedmaterial, or hydrated salt, as the case may be, on-site in the rundowntank 24. A body of molten salt is provided in the rundown tank 24,melting the salt in accordance with the aforementioned SECOND exemplarymethod if necessary. With the heat transfer 25 circulation loopinterrupted, the preheating circulation loop established, the rundowntank 24 vented and the pump 26 activated, a melting-point-alteringmaterial selected from among water, a hydrating fluid, and steam isadded to the fluid. When a rundown tank temperature sensor indicatesthat the body of salt in the rundown tank 24 is at a temperatureconsistent with sufficient hydration, or when a rundown tank hydrationmeasuring device 188 indicates sufficient hydration, the preheatingcirculation loop is interrupted and the processing circulation loop isestablished, and the aforementioned THIRD exemplary method can bepracticed.

With reference to FIG. 4, a FIFTH exemplary method of operating amolten-salt-indirectly heated screw-type thermal processor in accordancewith the present invention entails rehydrating the dehydrated salt, orre-making the melting-point-reduced material, as the case may be,on-site in the rundown tank 24 after ceasing processing and draining thefluid 25 to the rundown tank 24. This method is useful when it ispreferred to store liquid hydrated salt instead of letting dehydratedsalt solidify. The salt is rehydrated in accordance with theaforementioned FOURTH exemplary method, using the molten salt that wasdrained into the rundown tank 24.

With reference to any of FIGS. 1-7, a SIXTH exemplary method ofoperating a molten-salt-indirectly heated screw-type thermal processorin accordance with the present invention is carried out by carefullymanaging the performance of the pump 26 to avoid excess pressure. Thismay be done by measuring the pressure of fluid 25 arriving at thethermal processor 22, and delivering the heat transfer fluid 25 to thethermal processor 22 at a flow rate adjusted to effect the correction.

With reference to FIGS. 2-7, a SEVENTH exemplary method of operating amolten-salt-indirectly heated screw-type thermal processor in accordancewith the present invention is carried out by elevating the heat transferfluid 25 relative to the thermal processor 22 so as to establish agravity fluid 25 pressure head with the heat transfer fluid 25 enteringthe thermal processor 22 at a pressure at least within the operatingheat transfer fluid 25 pressure range. Thus, it becomes unnecessary tomodulate pump performance in order to ensure that fluid 25 is deliveredat adequate pressure to the thermal processor 22. As long as the fluid25 is capable of flowing and is being made available to flow downwardfrom the correct height into the heat transfer fluid inlet 38 of thethermal processor 22, there will be a predetermined pressure.

Also with reference to FIGS. 2-7, an EIGHTH exemplary method ofoperating a molten-salt-indirectly heated screw-type thermal processorin accordance with the present invention is carried out in accordancewith the aforementioned SEVENTH exemplary method, with the step, whiledelivering the fluid 25 to the thermal processor 22, of passivelydiverting the heat transfer fluid 25 to bypass the thermal processor 22in an amount sufficient to prevent the pressure exceeding the operatingheat transfer fluid 25 pressure range. The gravity tube upper drain 206fluidly communicating with the gravity tube 204 accomplishes this as dothe stem pipe 48 (fluidly connected to the gravity tube upper drain 206)and fill tank 30 (fluidly connected to the gravity tube 204).

When these methods are practiced with structure including a fill tank 30and a stem pipe 48, greater capacity is available to supply fluid 25 tothe thermal processor 22 during, e.g., a momentary interruption ofpumping.

Positioning the heat transfer fluid inlets 38 at elevations lower thanthose of the heat transfer fluid outlets 84 facilitates passive drainageof the heat transfer fluid space 32 at shutdown and clearance of gasfrom the heat transfer fluid space 32 when fluid 25 fills the heattransfer fluid space 32.

With a vacuum breaker 92 fluidly communicating with the heat transferfluid outlet 84 at a high elevation relative to the heat transfer fluidspace 32, and a vacuum breaker connector tube 93 fluidly connecting thevacuum breaker 92 with the rundown tank headspace portion 40, gaspressure and vacuum will not impede drainage of the heat transfer fluidspace 32.

Fluidly connecting the fill tank headspace portion 72 to the rundowntank headspace portion 40 avoids pressure differentials interfering withfilling and passive drainage of the fill tank 30 and the heater.

Limiting the operating heat transfer fluid 25 pressure range of thethermal processor 22 to between −12 PSIG and +14.9 PSIG, inclusive,avoids the need to fabricate the thermal processor 22 with a certifiedpressure boundary material.

Timing of delivery of fluid 25 to the thermal processor 22 isfacilitated, during melting, by measuring a temperature of the meltingmaterial and starting to deliver the fluid 25 via the heat transfer 25circulation loop when the measured temperature has reached apredetermined value, and alternatively by measuring the water content ofthe fluid 25 and starting delivery when the measured water content hasreached a predetermined value.

Timing of the addition of a hydration fluid to the heat transfer fluid25 is facilitated, during melting, by measuring a temperature of themelting material and beginning to add the hydration fluid when themeasured temperature has reached a predetermined value.

Steam must be vented from the heater 28 and rundown tank 24 duringhydration, and from the fill tank 30, via the gravity tube gas orifice208 to the rundown tank 24, during dehydration.

A NINTH exemplary method of operating a molten-salt-indirectly heatedscrew-type thermal processor in accordance with the present invention iscarried out by supplying a padding gas to the rundown tank headspaceportion 40 when the rundown tank headspace portion 40 isunderpressurized relative to the ambient environment, and venting a gasfrom the rundown tank head space portion 40 when the rundown tankheadspace portion 40 is overpressurized relative to the ambientenvironment. This management of gas pressure differentials preventsvapor lock, vacuum lock and rupture.

At shutdown, when the fluid 25 is passively draining to the rundown tank24, conducting a gas from the rundown tank headspace portion 40 to thethermal processor 22 fluid 25 outlet via the vacuum breaker 92 relievesvacuum lock in the thermal processor 22.

During start-up and continuous operation, conducting a gas from thethermal processor 22 head space 32 to the rundown tank headspace portion40 relieves vapor lock which could impede filling of the thermalprocessor 22.

Also in accordance with the present invention, with reference to FIG. 4,AN EXEMPLARY EMBODIMENT of a phase-separating pressure modulator formolten-salt-indirectly heated screw-type thermal processing apparatuscomprises a fill tank 30 having a fill tank bottom portion 36; a heateroutput tube 80 fluidly communicating with the fill tank 30 at the filltank bottom portion 36; a gravity tube 204 fluidly communicating withthe fill tank 30 at the fill tank bottom portion 36 and fluidlycommunicating with a fluid delivery destination such as the rundown tank24; a stem pipe 48 fluidly communicating with the fill tank 30 at anelevation above the fill tank bottom portion 36; a fill tank headspaceportion 72 defined as a portion of the fill tank above the elevationwhere the stem pipe 48 fluidly communicates with the fill tank 30; and afill tank headspace vent 73 or gravity tube gas orifice 208 fluidlycommunicating with the fill tank headspace portion 72 and with a fluiddrainage destination such as the thermal processor 22. Advantageously,during dehydration, when a mixture of molten salt and water vapor passesfrom the heater 28 to the fill tank 30, the fill tank separates thesteam from the molten salt under the influence of gravity, enabling thesteam to escape via the fill tank headspace vent 73 or gravity tube gasorifice 208 while the molten salt fluid 25 flows to the thermalprocessor 22, rundown tank 24 or both. While this function is performed,the previously described function of regulating the pressure of thefluid 25 at the heat transfer fluid inlets 38 of the thermal processor22 is also performed.

A pump 26 may refer to any energetic mechanism for urging or circulatinga material within the apparatus. A gravity tube gas orifice 208preferably fluidly communicates with the rundown tank headspace portion40, as, e.g., via a connector tube. While exemplary apparatus andmethods in accordance with the present invention may be claimed withrecitation of a molten-salt-indirectly heated screw-type thermalprocessor, the advantages of embodiments of the apparatus and instancesof the method in accordance with the present invention are applicablewithout strict limitation as to the composition of the heat transferfluid or as to the type of conveyance if any used in the thermalprocessor. The apparatus shown in any of FIGS. 1-3 and FIGS. 5-6 shouldbe regarded as being capable of having one or more heating elements 184as shown in FIG. 4 when and as needed. In most situations, the presenceof fire tubes 236 reduces the need for auxiliary heating of the rundowntank fluid containing portion 41. The apparatus shown in FIG. 3 shouldbe regarded as being capable of having a fill tank headspace vent 73(often useful to vent steam during heating) as shown in, e.g., FIG. 4.

As can be seen from the drawing figures and from the description, eachembodiment of the apparatus and method for fluid-heated indirect thermalprocessing in accordance with the present invention solves a problem byaddressing the need for safe, cost-effective, efficient, simple,reliable structure and steps in the thermal processing of materials.

While the specification describes particular embodiments of the presentinvention, those of ordinary skill can devise variations of the presentinvention without departing from the inventive concept.

Although specific embodiments have been illustrated and describedherein, those of ordinary skill in the art will appreciate that anyarrangement calculated to achieve same purposes can be substituted forthe specific embodiments shown. This disclosure is intended to cover anyand all adaptations or variations of various embodiments of theinvention. It is to be understood that the above description has beenmade in an illustrative fashion, and not a restrictive one. Combinationsof the above embodiments, and other embodiments not specificallydescribed herein will be apparent to those of skill in the art uponreviewing the above description. The scope of various embodiments of theinvention includes any other applications in which the above structuresand methods are used. Therefore, the scope of various embodiments of theinvention should be determined with reference to the appended claims,along with the full range of equivalents to which such claims areentitled.

In the foregoing description, if various features are grouped togetherin a single embodiment for the purpose of streamlining the disclosure,this method of disclosure is not to be interpreted as reflecting anintention that the claimed embodiments of the invention require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus the following claims,and such other claims as may later be added, are hereby incorporatedinto the description of the embodiments of the invention, with eachclaim standing on its own as a separate preferred embodiment.

The invention claimed is:
 1. A method of operating amolten-salt-indirectly heated screw-type thermal processor, the methodincluding the steps of: providing a molten-salt-indirectly heatedscrew-type thermal processor, said thermal processor having an operatingheat transfer fluid temperature range, an operating heat transfer fluidflow rate range and an operating heat transfer fluid pressure rangeproviding a body of heat transfer fluid, a heater, and a rundown tank,said heat transfer fluid being capable of conveying heat from saidheater to said thermal processor at a temperature within said operatingheat transfer fluid temperature range while flowing into said thermalprocessor at a heat transfer fluid flow rate within said operating heattransfer fluid flow rate range at a pressure within said operating heattransfer fluid pressure range, said heater being capable of heating saidheat transfer fluid to within said operating heat transfer fluidtemperature range at said flow rate and temperature, said body of heattransfer fluid having volume at least sufficient to operate with saidheater and said thermal processor, said rundown tank having capacitymore than sufficient to contain all of said body of heat transfer fluid;delivering said heat transfer fluid from said heater to said thermalprocessor at said temperature, said flow rate and said pressure whileallowing said heat transfer fluid to return from said thermal processorto said heater; after said steps of delivering, passively disposing saidbody of heat transfer fluid in said rundown tank; before said step ofdisposing, producing said heat transfer fluid by melting a solid; duringsaid step of melting a solid, circulating said heat transfer fluid insaid rundown tank.
 2. The method of claim 1, said heat transfer fluidcomprising a melting-point-altering material selected from among: ahydrating medium, a dopant.
 3. The method of claim 1, including, beforesaid step of disposing, a step of producing said heat transfer fluid byadding to a said heat transfer fluid a melting-point-altering materialselected from among: a hydrating medium, a dopant.
 4. The method ofclaim 3, said step of adding including a step of misting a hydratingmedium onto a surface of a body of said heat transfer fluid withoutdisrupting said surface.
 5. The method of claim 3, including, duringsaid step of adding, a step of circulating said heat transfer fluid insaid rundown tank.
 6. The method of claim 3, including, before said stepof adding, a step of melting a solid.
 7. The method of claim 1,including, after said step of disposing, a step of adding to said heattransfer fluid a melting-point-altering material selected from among: ahydrating medium, a dopant.
 8. The method of claim 7, including, duringsaid step of adding, a step of circulating said heat transfer fluid insaid rundown tank.
 9. The method of claim 1, wherein said heat transferfluid comprises a salt which is at least partially hydrated, the methodincluding, before said step of delivering is completed, a step of atleast partially dehydrating said salt.
 10. The method of claim 9,wherein said thermal processor has a predetermined maximum tolerablerate of temperature increase, said salt has a melting temperature whichincreases with decreasing hydration, and said step of dehydrating occursat a rate such that said thermal processor is warmed at a rate nogreater than said maximum tolerable rate of temperature increase. 11.The method of claim 1, said step of delivering including steps ofmeasuring said pressure, computing a correction of said pressure, anddelivering said heat transfer fluid to said thermal processor at a flowrate adjusted to effect said correction of said pressure.
 12. The methodof claim 1, said step of delivering including a step of elevating saidheat transfer fluid relative to said thermal processor so as toestablish a gravity fluid pressure head with said heat transfer fluidentering said thermal processor at a pressure at least within saidoperating heat transfer fluid pressure range.
 13. The method of claim 1,said operating heat transfer fluid pressure range being from −12.0 PSIGto +14.9 PSIG, inclusive.
 14. The method of claim 1, including, afterbeginning said step of melting, a step of measuring a temperature ofsaid heat transfer fluid being melted and a step of initiating said stepof delivering when said temperature has reached a predetermined value.15. The method of claim 6, including, during said step of melting, astep of measuring a temperature of said heat transfer fluid being meltedand a step of initiating said step of adding when said temperature hasreached a predetermined value.
 16. The method of claim 9, including,during said step of dehydrating, a step of venting steam from saidrundown tank headspace portion.
 17. The method of claim 1, wherein saidrundown tank has a rundown tank headspace portion, including a step ofsupplying a padding gas to said rundown tank headspace portion when saidrundown tank headspace portion is underpressurized relative to theambient environment and a step of venting a gas from said rundown tankheadspeace portion when said rundown tank headspace portion isoverpressurized relative to the ambient environment.
 18. The method ofclaim 17, wherein said padding gas is an inert gas.
 19. The method ofclaim 1, wherein said rundown tank has a rundown tank headspace portion,including, during said step of delivering, a step of conducting a gasfrom said thermal processor to said rundown tank headspace portion. 20.The method of claim 3, including, during said step of adding, a step ofmeasuring a melting-point-altering material content of said heattransfer fluid and a step of initiating said step of delivering whensaid material content has reached a predetermined value.
 21. A method ofoperating a molten-salt-indirectly heated screw-type thermal processor,the method including the steps of: providing a molten-salt-indirectlyheated screw-type thermal processor, said thermal processor having anoperating heat transfer fluid temperature range, an operating heattransfer fluid flow rate range and an operating heat transfer fluidpressure range providing a body of heat transfer fluid, a heater, and arundown tank, said heat transfer fluid being capable of conveying heatfrom said heater to said thermal processor at a temperature within saidoperating heat transfer fluid temperature range while flowing into saidthermal processor at a heat transfer fluid flow rate within saidoperating heat transfer fluid flow rate range at a pressure within saidoperating heat transfer fluid pressure range, said heater being capableof heating said heat transfer fluid to within said operating heattransfer fluid temperature range at said flow rate and temperature, saidbody of heat transfer fluid having volume at least sufficient to operatewith said heater and said thermal processor, said rundown tank havingcapacity more than sufficient to contain all of said body of heattransfer fluid; delivering said heat transfer fluid from said heater tosaid thermal processor at said temperature, said flow rate and saidpressure while allowing said heat transfer fluid to return from saidthermal processor to said heater; and after said steps of delivering,passively disposing said body of heat transfer fluid in said rundowntank; said step of delivering including a step of elevating said heattransfer fluid relative to said thermal processor so as to establish agravity fluid pressure head with said heat transfer fluid entering saidthermal processor at a pressure at least within said operating heattransfer fluid pressure range; said step of delivering including a stepof passively diverting said heat transfer fluid to bypass said thermalprocessor in an amount sufficient to prevent said pressure exceedingsaid operating heat transfer fluid pressure range.
 22. The method ofclaim 21, wherein: a fill tank fluidly communicates with said heater andwith said thermal processor; a stem pipe fluidly communicates with saidfill tank and with said rundown tank; said step of elevating includesaccumulating said fluid in said fill tank; and said step of passivelydiverting includes directing said fluid via said stem pipe to saidrundown tank.
 23. The method of claim 22, wherein: said fill tank has afill tank headspace portion; said rundown tank has a rundown tankheadspace portion; and a headspace connector fluidly communicates withsaid fill tank headspace portion and said rundown tank headspaceportion.
 24. A method of operating a molten-salt-indirectly heatedscrew-type thermal processor, the method including the steps of:providing a molten-salt-indirectly heated screw-type thermal processor,said thermal processor having an operating heat transfer fluidtemperature range, an operating heat transfer fluid flow rate range andan operating heat transfer fluid pressure range providing a body of heattransfer fluid, a heater, and a rundown tank, said heat transfer fluidbeing capable of conveying heat from said heater to said thermalprocessor at a temperature within said operating heat transfer fluidtemperature range while flowing into said thermal processor at a heattransfer fluid flow rate within said operating heat transfer fluid flowrate range at a pressure within said operating heat transfer fluidpressure range, said heater being capable of heating said heat transferfluid to within said operating heat transfer fluid temperature range atsaid flow rate and temperature, said body of heat transfer fluid havingvolume at least sufficient to operate with said heater and said thermalprocessor, said rundown tank having capacity more than sufficient tocontain all of said body of heat transfer fluid; delivering said heattransfer fluid from said heater to said thermal processor at saidtemperature, said flow rate and said pressure while allowing said heattransfer fluid to return from said thermal processor to said heater; andafter said steps of delivering, passively disposing said body of heattransfer fluid in said rundown tank; wherein: said thermal processor hasa heat transfer fluid inlet and a heat transfer fluid outlet; said heattransfer fluid inlet is at a lower elevation than said heat transferfluid outlet; in said step of delivering, said fluid enters said thermalprocessor via said heat transfer fluid inlet and exits said thermalprocessor via said heat transfer fluid outlet; and in said step ofdisposing, said fluid exits said thermal processor via said heattransfer fluid inlet.
 25. The method of claim 24, wherein: a vacuumbreaker fluidly communicates with said heat transfer fluid outlet; andin said step of disposing, a gas enters said thermal processor via saidvacuum breaker.
 26. The method of claim 25, wherein: said rundown tankhas a rundown tank headspace portion; and said vacuum breaker fluidlycommunicates with said rundown tank headspace portion.
 27. The method ofclaim 26, including, during said step of disposing, a step of conductinga gas from said rundown tank headspace portion to said thermal processorfluid outlet via said vacuum breaker.